IB Biology SL — All Flashcards

A molecule with an **uneven spread of charge** — a slightly negative end and a slightly positive end.

A bond in which two atoms **share a pair of electrons**.

How strongly an atom **pulls shared electrons** toward itself.

**Oxygen** — it is more electronegative, so it pulls the shared electrons closer.

The **two hydrogen** atoms.

A **partial** (slight) charge — much smaller than a full ionic charge.

About **104.5°** — the molecule is **bent**.

Its **bent shape** means the partial charges **do not cancel** — they act on the same side.

A **polar covalent** bond (electrons shared, but unequally).

It lets water molecules attract each other and other charged particles — the basis of water's life-supporting properties.

A **weak attraction** between a **δ+ hydrogen** of one water molecule and a **δ− oxygen** of another molecule.

**Between** separate water molecules (a covalent bond acts **within** one molecule).

A **δ+ hydrogen** of one molecule and a **δ− oxygen** of a neighbouring molecule.

Because each molecule is **polar** — it has a δ− oxygen and δ+ hydrogens.

**Weak** — much weaker than a covalent bond.

Because there are a **huge number** of them, so a **lot of energy** is needed to separate the water molecules.

A **strong** bond **within** a molecule, where atoms **share a pair of electrons** (the O–H bonds in water).

As a **dashed line** from a δ+ hydrogen of one molecule to the δ− oxygen of another, labelled **'hydrogen bond'**.

Water forms **many hydrogen bonds** that hold its molecules together; methane is **non-polar** and forms none.

High **boiling point**, **cohesion** (and a high **heat capacity**) — any two.

Yes — each molecule can hydrogen-bond to **several** neighbours at once.

A **partial** (slight) charge — much smaller than a full ionic charge.

The attraction of water molecules to **other water molecules** (water sticking to itself).

The attraction of water molecules to a **different surface** (water sticking to something else).

A 'skin-like' effect at the water surface, caused by **cohesion** pulling the surface molecules together.

**Hydrogen bonding** between water molecules, which happens because water is **polar**.

**Surface tension** (produced by **cohesion**).

**Adhesion** — water sticking to a different surface.

It holds water in an **unbroken column** in the xylem, so water can be pulled up from roots to leaves.

Water sticks to the **walls** of the narrow xylem vessels, helping support and lift the water column.

Cohesion + adhesion together let an unbroken water column be **pulled up the xylem** from roots to leaves.

**Adhesion** — the water sticks to the leaf surface.

**Cohesion** — water molecules pulling on each other at the surface.

Each bond is weak, but there are **so many** of them that together they hold the molecules tightly.

The amount of **heat needed to change the temperature** of a substance. Water's is **high**, so its temperature changes slowly.

Heating it must **break/stretch many hydrogen bonds** between the polar molecules, which takes a lot of energy.

The **heat needed to turn a liquid into vapour**. Water's is high, so evaporation removes a lot of heat.

Cooling caused because **evaporating water carries heat away** from the surface left behind (e.g. sweating).

Evaporating the sweat **takes heat from the skin** (high heat of vaporisation), lowering body temperature.

How well a material **lets heat pass through it**. Water conducts heat well, so it draws heat from a warm body.

Water's **high thermal conductivity** makes it lose body heat fast; **blubber insulates** against this.

Water's **high specific heat capacity** means its temperature changes only slowly, day and night.

The **hydrogen bonds** between polar water molecules — breaking them costs energy.

**Water changes far less** (high specific heat capacity); **air swings more widely**.

Water's **high specific heat capacity** — the sea releases a lot of heat for only a small temperature drop.

High **specific heat capacity**, high **heat of vaporisation**, and high **thermal conductivity**.

A liquid that **dissolves** another substance to form a solution. In cells the solvent is **water**.

A substance that **dissolves** in a solvent.

It is **polar** — its δ+ and δ− ends are attracted to charged/polar particles and surround them, pulling them into solution.

**Polar** molecules (e.g. glucose, amino acids) and **ionic** substances (salts, mineral ions).

**Non-polar** substances such as **fats and oils** (no charged parts for water to grip).

“Water-loving” — a **polar/charged** substance that **dissolves** in water.

“Water-fearing” — a **non-polar** substance that does **not** dissolve in water.

**Metabolism** (reactions between dissolved solutes) and **transport** (carrying dissolved substances).

In **xylem** (water + dissolved minerals) and **phloem** (dissolved sugars).

It is taken up by plants as **ions dissolved in soil water**, then passed to **animals that eat the plants**.

Low soil copper → grass takes up **little copper** → the animal eats that grass and takes in **too little copper**.

Roots absorb minerals as **ions in solution**, so the mineral must first **dissolve** in the soil water.

A **nucleotide**.

The monomer of a nucleic acid: a **phosphate group**, a **pentose sugar** and a **nitrogenous base** joined together.

A **phosphate group**, a **pentose (5-carbon) sugar**, and a **nitrogenous base**.

**Deoxyribose**.

**Ribose**.

**Thymine (T)**.

**Uracil (U)** — it replaces thymine.

**Adenine (A), cytosine (C) and guanine (G)**.

DNA is **double**-stranded (two); RNA is **single**-stranded (one).

**Sugar** (deoxyribose vs ribose), **one base** (thymine vs uracil), and **number of strands** (double vs single).

The **information-carrying** part of a nucleotide — A, C, G and either T (DNA) or U (RNA).

The sugar sits in the **middle** — joined to the **phosphate** on one side and the **base** on the other.

A **double helix** — two strands twisted around each other.

The rule that **A pairs only with T**, and **G pairs only with C**, on the two DNA strands.

**Thymine (T)**.

**Cytosine (C)**.

**Hydrogen bonds** (between the two bases).

**A–T has 2**; **G–C has 3**.

The **bases** (by hydrogen bonds). The sugar–phosphate backbones are not joined to each other.

The two strands run in **opposite directions** to each other.

In DNA, **%A = %T** and **%G = %C**.

**22%** — because %G = %C.

A = T = 30%, so A+T = 60%, leaving **40%** shared by G and C (20% each).

**Watson and Crick**, using X-ray data from **Rosalind Franklin**.

In the **sequence (order) of the bases** A, T, C and G along the molecule.

It is a **long** molecule using a **4-letter** code, so the bases can be ordered in an **enormous** number of ways.

The **order of the bases** (A, T, C, G) along a DNA strand — this order is the stored information.

Its two **complementary strands** back each other up, and the bases sit protected inside the double helix.

A **protein** that **DNA wraps around** to package (condense) it inside eukaryotic cells.

DNA **wraps around** them to **package / condense** the long molecule so it fits inside the cell.

A single long **DNA molecule wound around histones** and condensed into a compact, organised structure.

The DNA molecule is **very long** (about 2 m per human cell) but the cell is tiny, so it must be **condensed** to fit and be protected.

**Eukaryotes** (plants, animals, fungi). Most **prokaryotes do not** use histones.

The **order (sequence)** — rearranging the bases changes the message, like rearranging letters changes a word.

Like **thread around a spool** — the long thread winds up tightly and condenses.

**No** — histones only **package** the DNA. Reading and copying are done by other molecules.

**All of the DNA** of an organism — its complete set of genetic instructions.

Determining the **full order of bases** (A, T, C, G) across an organism's **entire genome**.

A **gene** is one instruction; a **genome** is the **whole instruction book** (all genes + the DNA between).

**No** — some plants and amphibians have larger genomes than humans but are not more complex.

Much of the extra DNA is **non-coding** — it does not code for proteins.

The same DNA bases code for the **same amino acids** in (almost) **every** living thing.

All life inheriting the **same code** is best explained by descent from a **common ancestor**.

The nucleus of **almost any single body cell** (e.g. a white blood cell).

A gamete (egg or sperm) carries only **half** the genome.

**Diagnosing genetic disease / personalising treatment**, and **comparing genomes to map how species are related**.

Concerns over **privacy** and how a person's **genetic data** is stored and used.

**Benefits AND a limitation/ethical concern**, then a clear overall **judgement**.

All living things are made of **cells**; the **cell is the basic unit** of life; new cells come only from **pre-existing cells**.

The (disproved) idea that living organisms can form from **non-living material**.

Broth in a **swan-neck flask** stayed clear; only when the neck was **broken** (letting air-borne microbes in) did it go cloudy — so cells come from cells.

The **cell** — there is no smaller living unit.

**Metabolism, Reproduction, Sensitivity, Growth, Respiration, Excretion, Nutrition** (MRS GREN).

**MRS GREN**.

The removal of the **waste products of metabolism** from a cell or organism.

Taking in (or making) the **food and nutrients** an organism needs.

An organism made of a **single cell** that carries out **all seven functions of life** by itself.

It is a complete organism with **no other cells to help**, so that one cell must do every job needed to stay alive.

Its **metabolism produces waste** (e.g. CO₂) that would **build up and become toxic** if not removed.

**Sensitivity**.

How many **times bigger** the image looks than the real object.

The ability to show two close points as **separate** — in short, how much **fine detail** can be seen.

Magnification = how much **bigger**; resolution = how much **detail**. Magnifying a blurry image just makes a bigger blur.

A beam of **light**.

A beam of **electrons**.

The **light microscope** — electron samples are killed and prepared first.

The **electron microscope** — much higher resolution than the light microscope.

Its **higher resolution** revealed **organelles and ultrastructure** not visible with the light microscope.

The **fine internal detail** of a cell (e.g. membranes, ribosomes) that only the electron microscope can reveal.

**Cryogenic electron microscopy** — it **freezes** a sample to capture a sharp snapshot of proteins and delicate structures.

**Cryo-EM** (a type of electron microscopy).

The sample must be **killed and specially prepared**, so you cannot view living cells.

**DNA, cytoplasm, plasma membrane and ribosomes** (memory hook: D-C-M-R).

A **specialised structure inside a cell** that carries out a **particular function** (for example a ribosome or nucleus).

**Ribosomes** — found in all cells and counting as an organelle.

It is the **genetic material** — the cell's stored instructions.

The **watery jelly** inside the cell where chemical reactions take place.

It is the cell's **outer boundary**, controlling what **enters and leaves**.

They **build proteins** by joining amino acids together.

**No** — prokaryotic cells have **no nucleus**; their DNA floats free in the cytoplasm.

The **nucleus** (in eukaryotes). **Mitochondria** also contain DNA, and **chloroplasts** do in plant cells.

Free in the **cytoplasm**, in a region called the **nucleoid** — there is no nucleus.

Any two of: **nucleus, cell wall, mitochondria, chloroplasts** (these are not universal).

A cell with **no nucleus** and **no membrane-bound organelles** (for example a bacterium).

A cell **with a nucleus** and membrane-bound organelles (for example animal, plant and fungal cells).

**Ribosomes** — universal and also an organelle; never answer 'nucleus'.

A cell with **no nucleus** and **no membrane-bound organelles**; its DNA lies free in the cytoplasm. All **bacteria** are prokaryotic.

A cell with a **true (membrane-bound) nucleus** holding the DNA, plus other membrane-bound organelles. **Animal, plant and fungal** cells are eukaryotic.

Prokaryotes have **no nucleus**; eukaryotes have a **true nucleus** enclosing the DNA.

As **one circular loop**, lying **naked** (no histones) in the cytoplasm, often with small extra rings (**plasmids**).

As **linear chromosomes** wound around **histones**, sealed inside the **nucleus**.

A **protein** that eukaryotic DNA wraps around to package its long chromosomes. Prokaryotic DNA has **no histones**.

A **small extra ring of DNA** in many prokaryotes, separate from the main DNA loop.

**Plasma membrane**, **cytoplasm**, **DNA** and **ribosomes**.

It rotates like a propeller to **move the cell** through liquid.

They are the site of **protein synthesis** (building proteins from amino acids).

Prokaryote ribosomes are **smaller (70S)**; eukaryote ribosomes are **larger (80S)**.

**Eukaryotic** (about 10–100 µm) vs **prokaryotic** (about 1–5 µm).

All are **eukaryotic** — they have a nucleus and membrane-bound organelles.

A **rigid layer outside the cell membrane** that gives a cell a fixed shape and support.

**Cellulose**.

**Chitin** (not cellulose).

**Animal cells** — they have only a flexible cell membrane.

**Chloroplasts** — the site of photosynthesis.

The plant cell has a **rigid cell wall** holding a fixed shape; the animal cell has **no wall**, so its membrane is easily squashed.

It is a fluid-filled sac that **keeps the cell firm**; animal cells have only small temporary vacuoles.

A cell that breaks the usual rule of having **one nucleus** — either anucleate or multinucleate.

A mature **red blood cell** — it **loses its nucleus**, leaving more room to carry oxygen.

**Skeletal muscle fibres** and **fungal hyphae** — one long cell with **many nuclei**.

A **photograph** of a specimen taken through a **microscope**.

A micrograph taken with an **electron microscope** — high enough magnification to see small organelles such as mitochondria.

A structure inside a cell that does a **specific job** (for example the nucleus or a mitochondrion).

Whether there is a **nucleus** — no nucleus means **prokaryotic**.

**No nucleus** and **no membrane-bound organelles**; the DNA lies **free in the cytoplasm**, and the cell is **small**.

It has a **nucleus** and **membrane-bound organelles** (such as mitochondria).

A **plant** cell has a **cell wall** and often **chloroplasts**; an **animal** cell has **neither**.

A **fungal** cell (its wall is made of **chitin**).

The **cell type** AND a **visible feature** as the reason (for example 'no nucleus, so prokaryotic').

The **double membrane (nuclear envelope)**, the **nuclear pores**, the **chromatin** and the **nucleolus**.

Because it is a **double membrane** — drawing a single line is the most common lost mark.

Small — about **1–5 μm** across (eukaryotic cells are usually much larger).

It is **oval** (sausage-shaped) with folded inner membranes called **cristae**.

**Rough ER** has membranes **studded with ribosomes** (dots); **smooth ER** has a **plain surface with no dots**.

It looks like a **stack of flattened, curved sacs**, often with small vesicles nearby.

A group of organisms that can **interbreed** and produce **fertile offspring**.

Defining a species by the ability to **interbreed** and produce **fertile offspring**.

Young that are themselves **able to reproduce**.

The offspring of a cross between **two different species** (e.g. a mule).

**Unable to reproduce** — cannot produce offspring of its own.

**No** — they produce a **mule**, which is **sterile**, so they are different species.

It leaves out that the offspring must be **fertile** — sterile young mean the parents are different species.

**Yes** — they can interbreed and give fertile pups; breed differences are just variation within one species.

An organism's full set of **chromosomes**, shown by their **number, size and shape**.

**Matching** chromosome number/pattern supports the **same** species; clearly **different** karyotypes suggest different species.

Organisms that **do not reproduce sexually** (e.g. bacteria) and **fossils**.

A **mule** — a sterile **hybrid**.

The system of naming each species with a **two-part Latin name**: **genus + species**.

The **first** word (it is capitalised), e.g. **Panthera** in **Panthera leo**.

The **second** word (it is lower-case); it only has meaning alongside its genus.

A group of **closely related species** — the first word of a scientific name.

In **italics**, with the genus **capitalised** and the species **lower-case**.

**Underline** each word (since you can't italicise by hand); genus still capitalised, species lower-case.

**Carl Linnaeus**, in the 1700s.

Linnaeus's idea of grouping organisms into species by their **shared physical features / appearance**.

They are **more closely related** than two species placed in **different genera**.

**Closely related** — they share the genus **Felis** (the same first word).

It has **no meaning without its genus** — different genera can reuse the same species word.

Common names vary between languages and regions; a binomial name is **one agreed name** for each species worldwide.

**Plants, animals, fungi and protists.**

An organism whose cells have a **nucleus** (and membrane-bound organelles).

**Cellulose.**

**Chitin.**

An organism that **makes its own food** from simple inorganic molecules (e.g. by photosynthesis).

An organism that obtains food by **taking in organic molecules** made by other organisms.

An organism that can feed as an **autotroph OR a heterotroph**, depending on conditions.

Heterotrophic feeding where food is taken **into the body and digested internally** (as animals do).

Heterotrophic feeding where enzymes digest **dead matter outside** the body, then the products are absorbed (as fungi do).

**Plants** (cellulose) and **fungi** (chitin) — same idea, different material.

**Autotrophic** — chloroplasts let it make its own food by photosynthesis.

They are the **'everything else'** eukaryotes — mostly **unicellular** and not fitting plants, animals or fungi.

A feature that **tells the group apart** from others (e.g. feathers for birds), not just any feature the organism has.

**Fur/hair** and **feeding young on milk** (from mammary glands).

**Feathers** and a **beak** (no teeth); they also lay hard-shelled eggs.

**Scales**, **gills** and **fins**; they live in water.

**Moist smooth skin**; they live partly in water and lay jelly-covered eggs in water.

Flowering plants have **true roots, vascular tissue and flowers/seeds**; mosses have **none** and reproduce by **spores**.

By **spores** — they have no flowers or seeds.

**Cnidarians** (e.g. jellyfish, sea anemones).

A **soft body**, often protected by a **shell** (e.g. snail, octopus).

A hard **exoskeleton** and **jointed legs** (e.g. insects, spiders, crabs).

A long body built from many similar **ring-like segments** (e.g. earthworm).

An animal with a **backbone** (a column of bones along its back).

A **common ancestor**. Groups meeting at a **more recent node** are **more closely related**.

**Molecular evidence** — comparing the **amino-acid sequence** of a shared protein (e.g. myoglobin) or the **DNA base sequence**. Fewer differences ⇒ more recent common ancestor.

They share **characteristics inherited from a common ancestor** — the shared rank reflects a recent common ancestry.

An identification tool made of **paired either/or choices** about observable features, each leading to another step or to an organism's **name**.

**Split into two** — every step offers exactly **two** opposite choices.

At **Step 1** (the top), then follow the matching choices in order.

A characteristic you can **see or measure** directly — e.g. legs, shell, scales, wings.

The key has reached the point that **names (identifies)** the organism.

**Two** — a pair of opposite either/or statements.

So every organism fits **exactly one** side at each step, with **no overlap**.

Habitat is **not a body feature** — a key must use features you can **observe** on the organism.

Follow **only the choice that matches** your organism, then go to the step or name it points to.

It shows the **correct path** for the marks and helps you **avoid careless slips**.

From its **observable features** — follow the key; never guess from the name.

One **numbered pair** of opposite statements; you pick the one that matches the organism.

A living organism whose **whole body is a single cell**.

A **life process every living organism must carry out** to stay alive (e.g. nutrition, response, reproduction).

**Nutrition, metabolism, growth, response, excretion, homeostasis, reproduction.**

It has **no tissues or organs** to share the work — the **one cell** must do everything itself.

**Nutrition** — taking in nutrients/food.

**Homeostasis** — it pumps out excess water to keep the internal water balance stable.

The water it removes entered by **osmosis** and is **not a metabolic waste** — excretion removes metabolic waste like CO₂.

**Excretion** — removing a waste product of metabolism.

**Response** — reacting to a stimulus in the surroundings.

Reproduction in which **one cell divides into two identical cells**.

**Reproduction** (by binary fission).

Any two of: **Paramecium, Amoeba, Euglena, Chlamydomonas, bacteria.**

The **change in the heritable characteristics of a population over generations** (a change in allele frequency).

**Heritable**, **population**, and **over generations**.

**Allele frequency** in the **gene pool** of a population.

One particular **version of a gene** (e.g. a dark or a light allele for fur colour).

How **common** a particular allele is in the gene pool (its proportion).

All the **alleles** present in a whole **population**.

**No** — evolution happens to a **population over generations**, not to one organism.

Only **genetic** features can be **passed to offspring** — learned or lifestyle changes are not inherited.

All the members of **one species** in an area that can **interbreed**.

**No** — it is a **non-heritable** change in **one individual** within its lifetime.

**Yes** — it is a heritable change in **allele frequency** of a **population over generations**.

Across **many generations** — not within a single lifetime.

Structures with the **same basic plan but different functions**, inherited from a **common ancestor** (e.g. human arm, bat wing, whale flipper).

Structures with a **similar function but a different basic plan** and no recent shared ancestor for that feature (e.g. bird wing vs insect wing).

One ancestral form gives rise to **several different forms** — it produces **homologous** structures.

Unrelated species under similar conditions evolve **similar features independently** — it produces **analogous** structures.

**DNA / base-sequence comparison** — more shared sequence means more closely related species.

**Homologous structures, fossils, biogeography, selective breeding and DNA base sequences.**

**Divergent** evolution — one common ancestor, then modified for different jobs.

**Convergent** evolution — similar features evolved separately under the same selection pressure.

It shows that **heritable characteristics of a population can change** quickly when there is selection — here, by humans.

Traits **gained during an organism's life are not heritable**, so they cannot be passed on; evolution acts only on heritable variation.

Homologous = **same plan, different job** (common ancestor); analogous = **same job, different plan** (convergent).

DNA is an **independent** clue — when a DNA cladogram agrees with one built from anatomy, two separate lines of evidence point to the same ancestry.

Trace both branches **back to the node where they meet**; the pair that join at the **most recent (lowest) node** share a common ancestor most recently, so they are the **most closely related**.

The **most recent common ancestor** of all the species above that point.

**Mutation**, **meiosis** and **sexual reproduction**.

**Mutation** — a random change to DNA. (Meiosis and sexual reproduction only make new combinations.)

The process where individuals **best suited to the environment survive and reproduce more**, passing on their alleles.

A **change in the heritable characteristics (allele frequencies)** of a population over many generations.

Only **gene-based (allele)** variation can be **passed to offspring**; traits gained during life are not inherited.

An **inherited feature** that makes an organism **better suited to its environment**.

A **favourable allele becomes more common** in the population over generations.

**No** — the variation is **already present** (mostly from past mutations); the environment only **selects** it.

More offspring are produced than can survive, so individuals **compete** — the best-suited ones win out and reproduce.

A few bacteria already carry a **resistance allele** (mutation); the antibiotic kills the rest; survivors **reproduce** and the allele becomes **more common**.

Some individuals **survive and reproduce more than others** because of their heritable features.

How **common a particular allele is** in a population.

A group of organisms that can **interbreed and produce fertile offspring**.

The formation of a **new species** from an existing one.

When two populations can **no longer interbreed** to produce fertile offspring.

The movement of **alleles between populations** through interbreeding.

Separation of populations by a **physical barrier** (river, mountain or ocean).

They can mate, but their offspring (a **mule**) is **sterile** — so they fail the 'fertile offspring' test.

Do a **breeding (crossing) test**: try to **interbreed** them and check whether the offspring are **fertile**. Fertile offspring ⇒ same species; no offspring or sterile offspring ⇒ different species.

(1) Populations become **reproductively isolated**; (2) they **diverge** by mutation and natural selection.

It **stops gene flow** between the two populations, allowing their gene pools to diverge.

**Mutation** (new alleles) and **natural selection** (different alleles favoured in each environment).

When they have diverged so much that they can **no longer interbreed to produce fertile offspring**.

All the **alleles present in a population**.

Divergence takes **many generations** of mutation and natural selection before interbreeding becomes impossible.

The **formation of a new species** from an existing one.

The **rapid evolution of many new species** from a single ancestor, each adapted to a **different niche**.

The particular **role and way of life** of a species — what it eats, where it lives and how it behaves.

Reaching **new, empty habitats** (for example a fresh island chain) with many unfilled niches.

A **sharp rise in the number of species** in one group over a relatively short time.

Speciation by the **slow build-up of small heritable changes** over a long time.

Speciation that happens **suddenly**, over a short time (for example by a **chromosome-number change**).

A **smooth series of in-between forms**, each only slightly different from the one before.

A **change in chromosome number**, which instantly stops the plant breeding with its parent population.

**Yes** — adaptive radiation, gradual and abrupt speciation all rely on **natural selection** and **reproductive isolation**.

One group **becoming more varied** — splitting into **many** different species over time.

The **variety of life** in an area — including **species, habitat and genetic** diversity.

The **number of different species** present in a community.

The ability of an ecosystem to **keep functioning and recover** after a disturbance.

**Species** diversity, **habitat** diversity and **genetic** diversity.

Species' roles **overlap**, so if one species is lost **another can cover its role** — the ecosystem keeps working.

It provides **food and materials**, **medicines**, and **ecosystem services** (e.g. pollination, water cleaning).

Free 'work' an ecosystem does for us — e.g. **bees pollinating crops** or wetlands cleaning water.

It is **irreversible** — a species' genes and its ecological role are gone **forever**.

**Habitat destruction**, **overexploitation** and **pollution** (also invasive species and climate change).

The current **rapid, human-driven** loss of species, happening far faster than the natural background rate.

Link **more species** to a **benefit** — usually greater **stability / resilience** or more **ecosystem services**.

You must **link** the extra species to a **consequence** (stability, services); the variety alone is not the mark.

The **variety of living organisms** — the number of different species and the variety within them.

The **permanent loss** of a species when its **very last member dies**.

**Habitat loss, overexploitation, pollution, invasive species, climate change** (memory hook: HIPPO).

**Habitat loss** — clearing a habitat removes the home of **every** species that depends on it at once.

Destruction or fragmentation of the **natural place a species lives** (e.g. deforestation, draining wetlands).

Harvesting or hunting a species **faster than it can reproduce**, so its population crashes.

A **non-native** species, introduced by humans, that spreads and **harms native species** by competing with, eating or infecting them.

Native island species often have **no defences** against a brand-new predator or competitor.

Harmful substances such as **pesticides or plastic** added to air, water or soil **poison or kill** wildlife.

Human-driven warming **shifts conditions faster than species can adapt** (e.g. coral bleaching as the sea warms).

**Extinction** = one whole species lost forever; **biodiversity loss** = the **wider fall** in variety, including shrinking populations.

**Named impacts with reasoning** (a direct and a knock-on effect) — not just 'it is bad'.

Protecting a species **within its natural habitat** (e.g. in a nature reserve or national park).

Protecting a species **outside its natural habitat** (e.g. in a zoo, botanic garden or seed bank).

**Nature reserves / national parks** and **wildlife corridors** that connect them.

The **whole ecosystem** is conserved together, so the species keeps a large population with **high genetic diversity** and behaves naturally.

A protected strip of habitat that **connects two separate reserves** so animals can move between them.

It lets animals **move, interbreed and recolonise** between reserves — keeping populations larger and genetically diverse.

The breaking up of one large habitat into **smaller, separated patches**.

The **harsher conditions** (wind, light, predators, invasive species) found **near the boundary** of a habitat patch compared with its interior.

A **large, rounded** reserve — it has **more sheltered interior** and **less exposed edge**.

It is **almost all edge**, so harsh edge conditions reach every part and few interior species survive.

The wild population stays **large**, so a wide range of alleles is kept (unlike a small captive group).

It conserves the **whole habitat/ecosystem** and lets the species **behave and evolve naturally**, not just survive in captivity.

Protecting a species **away from its natural habitat** — e.g. in a zoo, botanic garden, seed bank or gene bank.

Protecting a species **inside its natural habitat** — e.g. a nature reserve or national park.

**Captive breeding** (zoos), **botanic gardens**, and **seed / gene banks**.

Breeding endangered animals **under human care** to raise their numbers, often to **reintroduce** them to the wild.

A cold, dry store of seeds from many species kept as a **long-term genetic back-up**.

Animals breed **safely** (away from predators/poachers) under expert care, so the **population grows**.

They **preserve genetic variety** so a species can recover even if wild populations are lost.

**Releasing** captive-bred individuals back into a (protected) **natural habitat**.

It is **expensive** and holds **small numbers** (inbreeding risk); it also **does not protect the habitat**.

They may **lack survival skills** learned in the wild, so they can struggle to find food or avoid predators.

It keeps a species alive when its **wild habitat is too damaged**, but it does not protect that habitat — so it works **best alongside in situ**.

**In situ protects the habitat** (the species stays in the wild); **ex situ does not** (the species is held off-site).

Restoring the **natural processes** of a degraded ecosystem so it becomes **self-sustaining**, often by reintroducing a **keystone species**.

A species whose effect on its ecosystem is **far larger than its numbers** suggest (e.g. a top predator or a beaver).

An ecosystem that has been **damaged** so it works less well (e.g. a cleared forest or drained wetland).

Reintroducing a **keystone species** to restart natural processes across the ecosystem.

Restore natural **water flow** (re-flooding), re-establish natural **grazing**, let **native plants** return, or reconnect habitats with **corridors**.

Conservation protects species and often needs **ongoing management**; rewilding restores **natural processes** so the ecosystem **manages itself**.

Its activity (e.g. damming or predation) restarts a **chain** of natural processes that many other species depend on.

**Beavers** — they build dams that restore water flow and create wetland that supports many species.

Repairing a **damaged** ecosystem so its **natural processes** and **biodiversity** recover.

By restoring natural processes in a **degraded** ecosystem, it **reverses** damage so more species can return.

Any two of: **grazing**, **predation**, **flooding/water flow**, **seed dispersal**.

Restore a **natural process** (not just add a species) — e.g. re-flooding or letting native plants return.

**Evolutionarily Distinct and Globally Endangered**.

To **prioritise** which species to conserve — choosing those that are both distinct and endangered when resources are limited.

Having **very few close living relatives** — a unique, long branch on the tree of life carrying unique evolutionary history.

At **high risk of extinction worldwide** (e.g. a very small or fast-falling population).

A species that is **both** highly evolutionarily distinct **and** globally endangered — so it is high priority for conservation.

There are **more endangered species than money, land and time** to save them all, so choices must be made.

**No** — it is distinct but not at risk, so it is not urgent.

**No (lower)** — its loss is a smaller loss to the tree of life because similar species remain.

It removes a **unique branch of the tree of life and unique genes** that **no other species can replace**.

The **variety of life** — the range of different species (and genes and ecosystems) in an area.

**Protecting species and habitats** so that biodiversity is maintained for the future.

It must be **evolutionarily distinct AND globally endangered** — high on both, not just one.

**Four** — this lets carbon build chains, branches and rings.

Each carbon forms **four covalent bonds** and bonds to itself and other elements, so it builds a huge variety of molecule shapes.

A very large molecule built from **many smaller repeating subunits** (e.g. a polysaccharide, protein or nucleic acid).

A single small subunit that can be joined to others to build a larger molecule (e.g. glucose, an amino acid).

A large molecule made of **many monomers** joined together (e.g. starch).

A reaction that **joins two subunits** and **releases one water molecule (H₂O)**.

A reaction that **uses one water molecule (H₂O)** to break a bond and split a molecule into two subunits.

**Condensation** — it joins monomers and removes water.

**Hydrolysis** — it adds water to split the bonds.

**Anabolic** — it builds larger molecules from smaller ones.

**Catabolic** — it breaks larger molecules into smaller ones.

One **water molecule is released** (removed) each time a bond forms.

One **water molecule is used** (added) to break each bond.

They are macromolecules built from **smaller subunits joined by condensation**, releasing water.

'**Hydro**' = water, '**lysis**' = splitting — splitting a molecule using water.

A **single sugar unit** — the **monomer** of a carbohydrate (e.g. glucose, fructose, galactose).

A sugar made of **two monosaccharides joined together** (e.g. maltose, sucrose, lactose).

**C₆H₁₂O₆**.

Molecules with the **same chemical formula** but a **different arrangement of atoms**.

The **direction of the -OH group on carbon 1**: it points **down** in alpha-glucose and **up** in beta-glucose.

A reaction that **joins two molecules** together and **releases a molecule of water** (H₂O).

A reaction that **adds water** to **break a bond** — the reverse of condensation.

A **glycosidic bond**.

The disaccharide **maltose** **and** a molecule of **water**.

**Glucose + glucose**.

**Glucose + fructose**.

**Glucose + galactose**.

It is **small and soluble in water**, so it dissolves in the plasma and is carried around the body.

It is the **main respiratory substrate** — it is broken down in respiration to release energy (ATP).

A large molecule (polymer) made of **many monosaccharides** joined together.

**Glucose** — a monosaccharide.

**Starch** (energy store in plants), **glycogen** (energy store in animals), **cellulose** (structural support in plant cell walls).

**Alpha-glucose**.

**Beta-glucose**.

**Alpha-glucose** chains that are **coiled (helical) and lightly branched**.

**Alpha-glucose** chains that are **highly branched** (even more than starch).

**Beta-glucose** in **long, straight, unbranched chains** that hydrogen-bond into **fibres**.

It is a **large/compact glucose polymer** (lots of energy), **insoluble** (no effect on osmosis), and **branched** (many ends for fast glucose release).

It does **not dissolve**, so it does **not affect the cell's water balance** (osmosis) and stays as a store.

Branches give **many free ends**, so glucose can be **added or removed quickly** by hydrolysis when energy is needed.

Straight **beta-glucose** chains **hydrogen-bond** side by side into strong **fibres**, which support the **plant cell wall**.

It provides **structural support** — its fibres strengthen the **cell wall**.

We lack the enzyme to break its **beta-glucose** links, so it passes through as dietary **fibre**.

**Condensation** — each link **releases one water molecule (H₂O)**.

**One glycerol** joined to **three fatty acids**.

A small **3-carbon** molecule with **three —OH (hydroxyl) groups**; it forms the **backbone** of a triglyceride.

A long **hydrocarbon chain** ending in a **—COOH (carboxyl) group**, which is where it joins the glycerol.

An **ester bond**.

**Three** — one for each of the three fatty acids.

**Condensation** — it forms the ester bonds and **removes water** (one H₂O per bond, three in total).

**Hydrolysis** — it **adds water** (three H₂O) to break the three ester bonds.

**One glycerol** and **three fatty acids**.

Its carbon chain has **only single C–C bonds** — it holds the **maximum** hydrogen and the chain is **straight**.

Its chain has **one or more C=C double bonds**, which put a **kink** in the chain.

Look for a **C=C double bond** (and a **kink**) in the carbon chain.

Their **kinked chains** cannot pack closely together, so they stay **liquid**.

**Saturated** fats are usually **solid** (e.g. butter); unsaturated are usually **liquid oils** (e.g. olive oil).

**Three** — one per ester bond formed by condensation.

The **triglyceride** — one **glycerol** joined to **three fatty acids**.

In **adipose tissue** — fat-storage cells under the skin and around organs.

About **twice** as much energy **per gram**.

Their long **fatty-acid tails** contain many energy-rich **C–H bonds** and little oxygen.

**Insoluble** — the fatty-acid tails are **hydrophobic** (water-repelling).

Fat does not dissolve in the cell or draw water in by **osmosis**, so large amounts can be stored without upsetting the cell's water balance.

**Water-repelling** — a non-polar part that does not mix with or dissolve in water.

Animal tissue made of **fat-storage cells**; it stores triglycerides and forms an **insulating layer** under the skin.

**Thermal insulation** (slows heat loss) and **protection / cushioning** of organs.

Glucose has many polar **–OH groups** that attract water; a triglyceride's tails are **non-polar / hydrophobic**, so they do not.

**Lipid** (triglyceride fat) is the long-term, high-capacity store; **carbohydrate (glycogen)** is the short-term, quick store.

It holds lots of energy and carries no extra water, so it stores the **same energy for less mass**.

The energy-storage lipid: one **glycerol** molecule joined to **three fatty acids**.

**Pair it with its reason** — e.g. insoluble BECAUSE hydrophobic; high energy BECAUSE many C–H bonds.

A lipid made of **one glycerol, two fatty acids and a phosphate-containing head**.

Having **both a hydrophilic (water-loving) part and a hydrophobic (water-fearing) part** in the same molecule.

**Water-loving** — attracted to and mixes with water.

**Water-fearing** — does not mix with water; repelled by it.

The **phosphate group** (with the glycerol) — it is **polar**, so it is attracted to water.

The **two fatty-acid tails** — they are **non-polar**, so they are repelled by water.

Because the **same molecule** has a **hydrophilic head AND hydrophobic tails**.

By **condensation reactions** that join the fatty acids and phosphate to glycerol, **releasing water (H₂O)**.

Both use one glycerol, but a phospholipid has **2 fatty acids + a phosphate head**, while a triglyceride has **3 fatty acids and no phosphate**.

They **self-arrange into a bilayer**: hydrophilic heads face the water on both sides, hydrophobic tails tuck into the middle.

The **cell (plasma) membrane** — the boundary around every cell.

**Inwards**, towards the middle — away from the water on both sides.

A **triglyceride** (fully hydrophobic) or **glucose** (fully hydrophilic) — each is only one or the other.

**Glycerol** — the fatty-acid tails and the phosphate head all attach to it.

The **role** a species plays in its ecosystem — its **abiotic tolerances**, its **food source** and its **interactions** with other species.

**Abiotic tolerances** (e.g. temperature, oxygen), the **food/energy source**, and **interactions** with other species.

A **habitat** is *where* an organism lives (its 'address'); a **niche** is its *role* — how it lives (its 'job').

**Yes** — e.g. two fish in the same lake that feed on different foods have the same habitat but different niches.

A **non-living** physical condition of the environment, such as temperature, oxygen, light or pH.

A **living** influence on an organism, such as predators, prey, competitors or partner species.

The range of an abiotic factor (e.g. temperature) within which a species can **survive and grow**.

The **full** range of conditions and resources a species **could** occupy if there were **no competitors**.

The **smaller** part of the fundamental niche a species **actually** occupies once **competitors** are present.

Because **competition** restricts the species to part of its potential range (the start of competitive exclusion).

**Read the data** (e.g. temperature ranges) and deduce from the numbers — do not answer from general memory of the species.

Submerged plants are part of its niche — they provide **more shelter from predators** and **more food**, so the fish survives better there.

A **non-living** physical or chemical feature of the environment (e.g. temperature, light, water, pH, oxygen, salinity).

A **living** feature of the environment — the effect of other organisms (predators, competitors, parasites, food).

Ask **is it alive?** Non-living physical/chemical = abiotic; the effect of another organism = biotic.

**Temperature, light intensity and water availability** (also pH, oxygen, salinity, soil minerals).

**Predators, competitors and parasites** (also disease and food supply).

The range of an abiotic factor over which it can **survive** — best in the optimum, absent beyond its limits.

The middle peak, where the organism's **performance / abundance is highest**.

The organism cannot survive and is **absent**.

The abiotic factor **furthest from the optimum** — the one that restricts where an organism can live.

A **large region with a characteristic climate** (abiotic conditions) and a characteristic community of organisms.

**Temperature** and **rainfall** (water availability).

**Very high temperature** and **very low rainfall** (scarce water).

Conditions are kept **near its optimum**, so the **limiting factor is removed**.

Where an organism gets its **energy** and where it gets its **carbon**.

An organism that **makes its own organic carbon** from an inorganic source (**CO₂**). 'Auto' = self-feeding.

An organism that obtains organic carbon by **taking in organic molecules** made by other organisms. 'Hetero' = feeding on others.

An organism that can use **both modes** — making its own food like an autotroph AND taking organic food like a heterotroph (e.g. Euglena).

**Carbon dioxide (CO₂)** — an inorganic carbon source.

Both fix CO₂, but a **photoautotroph** uses **light** for energy, while a **chemoautotroph** oxidises **inorganic chemicals** (e.g. H₂S).

Heterotrophic feeding in which food is **ingested and digested INTERNALLY** inside the body (most animals).

A heterotroph that feeds on **dead** organic matter, digesting it **EXTERNALLY** with secreted enzymes and absorbing the products (decomposers).

A heterotroph that feeds on a **living host** and **harms** it (e.g. a tapeworm, a head louse).

Saprotroph digests **externally** and feeds on **dead** matter; a holozoic feeder ingests food and digests it **internally**.

Some bacteria around **deep-sea vents** that oxidise chemicals such as hydrogen sulfide for energy.

It is part of the niche: an **obligate aerobe** needs O₂, an **obligate anaerobe** is poisoned by it, a **facultative anaerobe** can use it or do without.

Read the **energy source AND carbon source together** — e.g. light + CO₂ = photoautotroph; oxidising chemicals + CO₂ = chemoautotroph.

Two species **cannot occupy exactly the same niche** in the same place indefinitely — one is excluded, or they partition the resource.

An organism's **role** in its ecosystem: the abiotic conditions it tolerates, the resources it uses and its interactions with other species.

The **full range** of conditions and resources a species **could** use if there were **no competitors** present.

The **smaller part** of the fundamental niche a species **actually** uses once **competition** from other species restricts it.

The realized niche is **never larger** than the fundamental niche — competition can only restrict it.

When the species grows **alone**, with **no competitors** present.

When the species grows **alongside a competitor**, which squeezes it into a smaller range.

When competing species **divide a shared resource** (by space, time or type) so each uses a different part and they can **coexist**.

**Competitive exclusion** (one species is driven out) or **resource partitioning** (they split the resource and coexist in separate zones).

Each is the **better competitor in a different part** of the gradient and **excludes** the other from the part it loses, so each is restricted to its **realized niche**.

**Competition** between them — each has excluded the other from part of the gradient (competitive exclusion / partitioning).

An interaction where two **different species** both need the **same limited resource**, so each reduces the amount available to the other.

An interaction between **two different species** ('inter' = between, 'specific' = species).

By the **effect on each species**: **+** if it benefits, **–** if it is harmed.

One organism (the **predator**) kills and eats another (the **prey**). Predator **+**, prey **–**.

An animal eats a plant (or part of one). The herbivore **+**, the plant **–** (often not killed).

Two species use the same **limited resource**, so **both are harmed** ( **– / –** ).

Two species live closely together and **both benefit** ( **+ / +** ).

A **parasite** lives on or in a **host**, taking nutrients. Parasite **+**, host **–**.

A **pathogen** (disease-causing microbe) infects a host and causes **disease**. Pathogen **+**, host **–**.

**Mutualism** ( **+ / +** ) — e.g. a bee pollinating a flower; legume + nitrogen-fixing bacteria.

**Competition** ( **– / –** ) — it is the only – / – relationship.

By **how** the harm happens: **eaten** → predation/herbivory; **lived on / infected** → parasitism/pathogenicity.

**Name** the relationship **and** state how **each** species is affected (+ / –). Naming alone scores only half.

**Mutualism** — both the human and the bacteria benefit.

**Mutualism** — the plant gains usable nitrogen and the bacteria gain sugars and a habitat.

The **monomer (subunit)** that **proteins** are built from.

An **amino group (—NH₂)**, a **carboxyl group (—COOH)**, a **hydrogen (—H)** and a **variable R group**.

The **amino group (—NH₂)** — a nitrogen-containing group.

The **carboxyl group (—COOH)**.

The **variable side chain** of an amino acid — the only part that differs from one amino acid to the next.

**20** — because there are **20 different R groups**; the rest of the structure is identical.

The **central carbon**, the **amino group**, the **carboxyl group** and the **hydrogen** — only the R group differs.

**Carbon, hydrogen, oxygen and nitrogen** (some also contain sulfur).

From the **amino group (—NH₂)**.

A protein contains **nitrogen**; carbohydrates and lipids contain only **C, H and O**.

**No** — they contain only carbon, hydrogen and oxygen. Nitrogen is found in proteins / amino acids.

**One** — all four groups attach to this single central carbon.

**Condensation** — it forms a **peptide bond** and releases one water molecule.

The covalent bond (**CO—NH**) that joins two amino acids; it forms by condensation.

The **carboxyl group (—COOH)** of one amino acid and the **amino group (—NH₂)** of the next.

An **—OH** (from the carboxyl group) and an **—H** (from the amino group), leaving together as **one water molecule**.

**One** molecule of water (H₂O) per peptide bond.

**Two amino acids** joined by a single peptide bond.

A long chain of **many amino acids** joined by peptide bonds.

**Hydrolysis** — one water molecule is **added** across the bond, splitting the chain into amino acids.

During **digestion**, when dietary protein is broken back down into amino acids.

**n − 1** — each bond links a pair, so there is one fewer bond than amino acids.

**Total amino acids − number of chains** (each chain has one fewer bond than its amino acids).

**4** (5 − 1).

**20** — about **nine** are essential and about **eleven** are non-essential.

An amino acid the body **cannot synthesise (make)**, so it **must be obtained from the diet**.

An amino acid the body **can synthesise (make)** for itself, so it **does not have to be supplied by the diet**.

**No** — every amino acid is needed to build proteins. 'Non-essential' only means it is **not required in the diet**, because the body can make it.

To **make / build** a molecule inside the body from simpler materials.

**Essential** amino acids — the body cannot make them.

**Essential = cannot be made by the body → must be eaten**; **non-essential = can be made by the body → need not be eaten**.

They contain **all nine essential amino acids** in a single source (meat, fish, eggs, dairy).

A single plant protein often **lacks one or more essential amino acids**.

**Combine different plant proteins** (e.g. rice + beans) so that **all nine essential amino acids** are supplied.

The body has **no source** of it, so it **cannot build the proteins** that contain it (a protein deficiency).

It **cannot be synthesised by the body**, so it **must be obtained from the diet**.

Its specific **folded 3D shape**. The protein only works correctly in its normal conformation.

The **sequence (order) of its amino acids** — the primary structure.

The **sequence (order) of amino acids** in the chain, joined by peptide bonds.

Local folding into **α-helices** (coils) and **β-pleated sheets**, held by **hydrogen bonds**.

The way the **whole single chain folds** into one overall **3D shape**, held by bonds between the R-groups.

The way **two or more folded chains (subunits)** join together to make one functional protein (e.g. haemoglobin).

**Primary → secondary → tertiary → quaternary.**

**Single-chain** proteins — quaternary structure needs **two or more** chains.

**Hydrogen bonds** between parts of the polypeptide backbone.

The **loss of a protein's folded 3D shape**, so it can no longer do its job.

**High temperature** and **extreme pH** (very acidic or alkaline).

The **amino acid sequence (peptide bonds) is preserved**; the **folded 3D shape (conformation) is lost**.

Its **active site changes shape**, so the **substrate no longer fits** and the reaction is not catalysed.

Its specific **3-D shape**, which comes from the **order of its amino acids**.

Proteins, as a group, can carry out a very **wide range of different jobs** — more than any other type of molecule.

**Amylase** — it **catalyses** the breakdown of starch into sugar.

**Haemoglobin** — it **carries oxygen** in red blood cells.

**Collagen** — it strengthens **skin, tendons and bone**.

**Insulin** — it signals cells to **take up glucose** from the blood.

**Defence** — they **bind to specific pathogens** so the body can destroy them.

**Actin and myosin** — contractile proteins that generate **movement**.

**Rhodopsin** — it **absorbs light** in the rod cells of the retina (needed for vision).

A **shortage of, or fault in, a particular protein**, so the job it normally does cannot be carried out.

Name the **protein's job**, then state that this **job is lost** — so the process that relied on it **fails**.

A shortage of **rhodopsin** — it normally **absorbs light** in rod cells, so without it light is not detected and vision is impaired.

The 20 amino acids can be **ordered in countless ways**, giving countless **shapes** — each shape gives a different **function**.

A **phospholipid bilayer** — two rows of phospholipids — with proteins, glycoproteins and cholesterol embedded.

Having **both** a hydrophilic (water-loving) part and a hydrophobic (water-hating) part in the same molecule.

The **phosphate head** is hydrophilic (water-loving); the **two fatty-acid tails** are hydrophobic (water-hating).

They are **attracted to the water** present on both the outer and inner surfaces of the membrane.

They are **repelled by water**, so they are pushed into the centre, away from the water, forming the core.

Because phospholipids are amphipathic and there is **water on both sides**: heads go to the water, tails away from it, giving two rows.

It makes the membrane **selectively permeable** — small non-polar molecules pass, but large/polar molecules cannot cross freely.

Acts in **cell recognition** and cell signalling — its carbohydrate chain on the outer surface is an 'identity tag'.

Wedges between the phospholipids and **stabilises fluidity**, reducing leakiness to small molecules.

**Fluid** because phospholipids and many proteins drift sideways; **mosaic** because different molecules are dotted through the bilayer like tiles.

Davson–Danielli put **two continuous protein layers** coating the bilayer; the fluid mosaic model **scatters proteins through** it.

Electron-microscopy images showing **proteins embedded within** the bilayer, not just coating its surfaces.

**Integral** proteins are embedded right through the bilayer (e.g. channels, carriers); **peripheral** proteins rest on one surface.

Movement across a membrane that needs **no energy (ATP)** — particles move **down a gradient** on their own.

The **net movement of small or non-polar particles** down their concentration gradient, **straight through the phospholipid bilayer**.

The net movement of **water** across a **partially permeable membrane**, from **higher water potential (dilute) to lower (concentrated)**.

**Small, non-polar** molecules — e.g. **O₂, CO₂** — and **lipid-soluble** molecules such as **steroid hormones**.

The bilayer's core is **non-polar / hydrophobic**, so non-polar molecules are **not repelled** — they dissolve in and pass through.

They are **repelled by the hydrophobic core** (or too large), so they need a **protein** to cross.

From the **more dilute** solution to the **more concentrated** one (high → low **water potential**).

A measure of how free the water is to move. **Pure water is highest**; adding solute lowers it. Water moves from **high to low** water potential.

A **channel protein** that lets water cross **quickly**, speeding up osmosis. It uses **no ATP** and doesn't change the direction.

**Passive** — it uses no ATP, even when aquaporins speed it up.

A **steeper** gradient gives a **faster** rate of net diffusion; a shallower one gives a slower rate.

Water is **entering** the cell (net water movement in), so the outside solution is **more dilute / hypotonic**.

Water is **leaving** the cell (net water movement out), so the outside solution is **more concentrated / hypertonic**.

A **higher temperature** and a **larger membrane surface area**; a **thicker** membrane slows it down.

The **passive** movement of **ions and large polar molecules** across a membrane through a **channel or carrier protein**, **down the concentration gradient** (no ATP).

They are **large/polar or charged**, so they are repelled by the **hydrophobic (water-hating) core** of the bilayer — they need a transport protein.

A membrane protein with an **open water-filled pore** that lets specific ions or polar molecules pass **straight through**.

A membrane protein that **binds** a specific molecule and **changes shape** to move it across the membrane.

A channel is an **open pore** (fast; ions, water); a carrier **binds and changes shape** (slower; glucose, fructose).

**Down the concentration gradient** — from **high** to **low** concentration.

**No** — it is **passive**, because particles move down their concentration gradient.

The **route**: simple diffusion goes **straight through the bilayer**; facilitated diffusion goes **through a protein**. Both are passive and down the gradient.

A **channel protein** (an open pore).

A **carrier protein** (it binds and changes shape).

The transport proteins become **saturated** — every channel/carrier is occupied, so the rate reaches a **maximum** and cannot rise further.

Aquaporins are **channel proteins** for **water** — water crosses through them by facilitated diffusion (a fast, passive route).

The movement of a substance **against** its concentration gradient, using energy from **ATP**.

Active transport moves particles **against** the gradient and **uses ATP**; diffusion is passive — **down** the gradient with **no ATP**.

A **pump protein** (the protein responsible for active transport).

**'Against' the gradient** and **'uses ATP'** — either one signals active transport.

Pumps **3 sodium ions (Na⁺) out** of the cell and **2 potassium ions (K⁺) in**, both against their gradients.

**Sodium (Na⁺) OUT**, **potassium (K⁺) IN**.

Because ions constantly **leak back** down their gradients; the pump keeps replacing them to **maintain** the gradients.

By **active transport** — the Na⁺/K⁺ pump uses **ATP** to keep moving ions against their gradients.

The pump stops, ions keep leaking back, and the gradients gradually **even out**.

It **needs energy** — it always uses **ATP**.

**Simple diffusion**, **facilitated diffusion** (both passive) and **active transport** (active, uses ATP).

Uptake of **mineral ions by plant root cells** against their concentration gradient.

The membrane lets **some substances cross but blocks others**, mainly depending on their **size** and whether they are **polar**.

**Small, non-polar** molecules such as **oxygen** and **carbon dioxide** (water crosses too, helped by aquaporins).

**Large** molecules such as **starch** and **proteins** — they are too big to pass through.

As a **model** of a partially permeable membrane: its pores let **small** molecules through but hold back **large** ones.

**Glucose passes out** through the pores (it is small); **starch stays inside** (it is too large).

Its molecules are **too large** to fit through the pores of the partially permeable tubing.

Moving **large amounts of material**, or particles too big to cross the bilayer, **in vesicles** — it **uses ATP**.

Bulk transport that brings material **INTO** the cell: the membrane **folds inwards** and pinches off a vesicle around the material.

Bulk transport that releases material **OUT** of the cell: a vesicle **fuses** with the plasma membrane and empties its contents.

**Yes** — both endocytosis and exocytosis **use ATP**, so bulk transport is **active**.

Taking in **large food particles** or engulfing a **pathogen** (e.g. a white blood cell engulfing a bacterium).

**Secreting** proteins, **enzymes** or **hormones** (e.g. a gland cell releasing a digestive enzyme).

**Endo** = **into** the cell ('enter'); **exo** = **exit** the cell.

A structure inside a cell that carries out a **specific function** (a 'little organ').

An organelle **surrounded by its own membrane** (e.g. nucleus, mitochondrion, Golgi apparatus).

It **holds the cell's DNA** and **controls** the cell's activities.

It is the site of **aerobic respiration**, releasing **energy (ATP)** for the cell.

It **builds proteins** by joining amino acids (protein synthesis).

The **ribosome** — it is the only organelle without a membrane.

It **makes and transports proteins** (its surface is studded with ribosomes).

It **modifies, packages and sorts proteins** into **vesicles** for transport or export.

The **Golgi apparatus**.

**Ribosomes / rough ER → Golgi apparatus → vesicle** (build → package → transport out).

If it is a **membrane-bound organelle** — prokaryotes have no membrane-bound organelles, only ribosomes.

Its correct **name** AND a **specific function** (a vague function scores no marks).

**Dividing the inside of the cell into separate membrane-bound spaces** (compartments) — most are the membrane-bound organelles.

An organelle surrounded by its own membrane (e.g. nucleus, mitochondrion, lysosome), creating a **compartment** separate from the cytoplasm.

It **separates incompatible reactions** (or: concentrates enzymes/substrates; encloses harmful substances; adds membrane surface; keeps local optimum conditions).

The molecules for a reaction are gathered in a **small space**, so the reaction happens **faster**.

The membrane keeps the enzymes **separate**, so they **cannot digest or damage the rest of the cell**.

They provide extra **membrane surface area** for membrane-bound reactions (e.g. the folded inner membrane of a mitochondrion).

**More of an organelle = more of its job** — a cell that does a lot of a process has a lot of the organelle that carries it out.

A lot of **aerobic respiration** to release **ATP** — so the cell is very **active** (e.g. a muscle cell).

A lot of **making and processing molecules** (proteins, lipids, detoxification) — e.g. a liver cell.

**Link structure to function** — state what organelle X does, then say the cell does a **lot** of that process.

The mark is for the **link** between the feature and the cell's function, not for the label itself.

**No** — they have no membrane-bound organelles, so their reactions share one space (the cytoplasm).

**DNA, cytoplasm, a plasma membrane and ribosomes** — present in both prokaryotes and eukaryotes.

A **structure inside a cell** that carries out a particular job (e.g. nucleus, mitochondrion, chloroplast).

A cell with **no nucleus and no membrane-bound organelles**; its DNA is free in the cytoplasm (e.g. a bacterium).

A cell that keeps its DNA inside a **nucleus** and contains **membrane-bound organelles** (e.g. animal, plant, fungal cells).

The **nucleus** — prokaryotes have none (DNA free in the cytoplasm); eukaryotes enclose their DNA in a nucleus.

A **chloroplast** (also acceptable: large central vacuole, or cellulose cell wall).

**Ribosomes** (also: plasma membrane, DNA, cytoplasm).

A **cellulose cell wall**, **chloroplasts** and a **large central vacuole**.

**Yes** — both are eukaryotic, so both have a nucleus, mitochondria, ribosomes and a plasma membrane.

Because plants (cellulose), fungi (chitin) and most bacteria (peptidoglycan) all have cell walls — the material differs.

A **fungal cell** — eukaryotic with a wall, but no chloroplast (so not a plant).

No nucleus → **prokaryote**; nucleus + chloroplast → **plant**; nucleus, no chloroplast → **animal**.

**Eukaryotic** cells are larger (about 10–100 µm); prokaryotes are smaller (about 1–5 µm).

Mitochondria and chloroplasts began as **free-living prokaryotes** that were **engulfed** by a host cell and **survived inside it**, becoming organelles.

'**Endo**' = inside, '**symbiosis**' = living together — one cell living permanently inside another, with both benefiting.

An **aerobic (oxygen-using) bacterium** — it carries out aerobic respiration to release energy for the host.

A **photosynthetic bacterium** — it makes food using light, in plant and algal cells.

**Engulf** the bacterium -> it **survives** inside -> the relationship **benefits both** -> the bacterium is **kept** and becomes an organelle.

**Endocytosis** — the host membrane folded around the bacterium, so it ended up inside a vesicle.

Each organelle has its **own DNA**, its **own 70S ribosomes**, a **double membrane**, and divides by **binary fission**.

**70S** — the smaller, bacterial type. The host cell's cytoplasm uses larger **80S** ribosomes.

The **inner** membrane is the bacterium's own; the **outer** membrane came from the host's vesicle when the bacterium was engulfed.

The cytoplasm uses **80S** ribosomes, but the chloroplast keeps the **70S** ribosomes of its free-living bacterial ancestor.

By **binary fission** — splitting in two on their own, just like the free-living bacteria they descended from.

Only some cells engulfed the **photosynthetic** partner (-> chloroplast); the **aerobic** partner (-> mitochondrion) was engulfed by the ancestor of nearly all eukaryotes.

The process by which an **unspecialized cell** develops into a **specialized cell** with a particular structure and function.

A cell that has **no particular job yet** and can still develop into different cell types (e.g. a stem cell).

A cell with a **particular structure suited to one particular function** (e.g. a neuron or red blood cell).

**Differentiation**.

**Differentiation** — it produces the specialized cell types that group into tissues.

**Cell division (mitosis)** makes **more** cells (identical copies); **differentiation** makes cells **different** (specialized).

**Cell division (mitosis)** — it makes more identical cells.

**Differentiation** — it makes cells become different from one another.

First **cell division** makes many identical cells, then **differentiation** makes them into specialized types.

So cells can **specialize for one job each** (division of labour), letting the whole organism do many jobs efficiently.

From **'different'** — it makes cells become **different from one another** (specialized).

**Yes** — they all came from the same original cell and share the same genes, but they differentiated into different types.

The process by which an **unspecialized cell becomes a specialized cell** with a particular structure and function.

**Yes** — every body cell carries the same complete set of genes (the same genome).

**Different genes are expressed** (switched on) in each cell type — not different genes present.

Switching a gene **'on'** so it is used to make its **protein**. An expressed gene is active; an unexpressed gene is silent.

Expressing **only some** of the genes in the genome — different genes in different cell types — so each cell makes only the proteins it needs.

**Chemical signal gradients** — the concentration of signalling molecule a cell meets depends on its **position**.

A smooth change in the concentration of a signalling molecule — **high near its source**, lower further away.

A cell's **position** sets the **signal concentration** it meets, which switches on a **particular set of genes**, deciding the cell type it becomes.

It **differentiates** — switching on specific genes and becoming a specialized cell type.

The genes switched on are used to make **specific proteins**, which give the cell its specialized **structure and function**.

**No** — unused genes are switched **off**, not removed. The cell keeps the full genome.

Position in gradient → **signal concentration** detected → **genes** switched on → **proteins** made → specialized **cell type**.

An **unspecialized** cell that can **self-renew** (keep dividing) and **differentiate** into specialized cell types.

**Self-renewal** (divides to make more stem cells) and **differentiation** (becomes specialized cells). Both are needed.

A measure of **how many different cell types** a stem cell can differentiate into.

Can become **any cell type plus the placenta**. Example: the **zygote** / very early embryo.

Can become **any cell type of the body** (but not the placenta). Example: **embryonic stem cells**.

Can become a **limited family of related** cell types. Example: **blood-forming cells in red bone marrow**.

Can become **only one** cell type.

**Totipotent** cells can also form the **placenta**; **pluripotent** cells cannot.

Potency **decreases** (and specialization increases) as cells differentiate — adult stem cells are usually only multipotent or unipotent.

The **location in the body** where a particular stem cell is found (e.g. red bone marrow for blood-forming stem cells).

**Multipotent** (forms the family of blood cells); niche = the **red bone marrow**.

In the **early embryo** — they are the **embryonic stem cells**.

An **unspecialized** cell that can **divide (self-renew)** and **differentiate** into one or more specialized cell types.

They can **divide** to make many cells, and they can **differentiate** into the specialized cell type that is needed.

A stem cell's ability to **divide by mitosis** to make more cells (including more stem cells), so the supply is not used up.

The process by which an **unspecialized** cell becomes a **specialized** cell with a particular structure and function.

They **divide** to make many new cells, then **differentiate** into the exact lost cell type, replacing the missing cells and restoring function.

Because they can **divide** to make enough cells and **differentiate** into the specific specialized cell that was lost.

From **very early embryos**; they can become **almost any** cell type (very flexible).

From **body tissues** such as **bone marrow**; they can become only a **few** related cell types.

They are taken from an **early embryo**, which would otherwise develop — this raises **ethical objections**.

**No embryo is used** — they are taken from body tissues, often from the patient themselves.

**Replacing cells lost to disease or injury** (e.g. blood, nerve or skin cells) that the body cannot regrow on its own.

A **rise in cell number** shows **division**; the appearance of **named specialized cells** shows **differentiation**.

A cell whose **structure is adapted** to carry out a **particular function** efficiently.

By **differentiation** — switching on (expressing) a particular set of their genes.

**Structure follows function** — a cell's shape and contents match the job it does.

**Biconcave** shape (large surface area) and **no nucleus** → more room for **haemoglobin** to carry O₂.

**Microvilli** give a large **surface area**; **many mitochondria** supply **energy (ATP)** for active transport.

A **tail (flagellum)** and many **mitochondria** → energy to **swim** to the egg.

A very **long fibre (axon)** → carries **electrical impulses** over long distances.

**Column shape near the upper leaf surface**, packed with **chloroplasts** → absorbs the most **light**.

A **long, thin projection** into the soil → large **surface area** to absorb **water and minerals**.

The **egg cell (ovum)** — it stores **food reserves** for the early embryo.

The **sperm cell** (stripped down to swim) and the **red blood cell** (small and flexible for capillaries).

In **feature → function pairs** — name a structure AND the job it makes possible; one mark per linked pair.

A cell that fits the standard description: **one nucleus**, **microscopic** size, and its **own sealed membrane** (and wall in plants/fungi).

A cell that **does not fit the typical description** — e.g. it lacks a nucleus, has many nuclei, is unusually large, or shares its cytoplasm.

Having **no nucleus**. ('a-' = without.)

Having **many nuclei** inside one cell or fibre. ('multi-' = many.)

Having **no cross-walls (septa)**, so the cytoplasm is **continuous** — seen in some fungal hyphae.

A **mature mammalian red blood cell** and a **phloem sieve tube element** — both lose their nucleus.

A **skeletal (striated) muscle fibre** — many cells **fuse** into one long fibre with many nuclei.

To leave **more room for haemoglobin**, so it can **carry more oxygen**.

It breaks the rule that cells are microscopic — a **single cell** can be **several centimetres long**.

It has **no cross-walls**, so the **cytoplasm is continuous** and **many nuclei are shared** along the thread.

**Adaptations** — each unusual feature usually helps the cell do a **specific job**.

**Zero** nuclei = anucleate; **many** nuclei = multinucleate; **one** nucleus = typical.

The thin boundary where gases pass between the body and the environment — e.g. the wall of an **alveolus** in the lung.

**Diffusion** — the passive net movement of particles from **high** to **low** concentration.