Transfers of energy and matter

An organism that **makes its own organic molecules** from inorganic substances (e.g. CO₂), using an external energy source. 'Auto' = self.

An organism that **cannot make its own organic molecules** and must take in ready-made organic food from other organisms. 'Hetero' = other.

**Inorganic carbon dioxide (CO₂)** — they fix it into organic molecules.

From **light** (photosynthesis). Examples: plants, algae, cyanobacteria.

By **oxidising simple inorganic substances** (chemosynthesis). Examples: deep-sea vent bacteria.

Only in their **energy source** (light vs oxidising inorganic substances); both fix **CO₂** for carbon.

Heterotrophic nutrition where food is **ingested** and **digested internally** — the way animals feed.

A heterotroph that feeds on **dead or decaying** matter by releasing enzymes onto it and absorbing the products — **external digestion** (many fungi/bacteria).

An organism that uses **both** autotrophic and heterotrophic nutrition — it can make its own food and feed on others (e.g. Euglena).

**Autotrophs** — they produce organic molecules that feed the heterotrophs.

The **energy source** and the **carbon source** of the organism.

**Outside** its body (external digestion) — then it absorbs the digested products.

A diagram showing a **single path of energy** through an ecosystem, drawn as organisms joined by **arrows**.

**Several food chains linked together**, showing the many feeding relationships in an ecosystem more realistically.

An organism's **feeding position** in a food chain (e.g. producer, primary consumer, secondary consumer).

From the organism **being eaten** to the organism that **eats it** — the direction **energy flows** ('is eaten by').

**Producer** (1) → **primary consumer** (2) → **secondary consumer** (3) → **tertiary consumer** (4).

An organism that makes its own food by **photosynthesis** (an autotroph); it is always the **first** trophic level.

A **herbivore** — an organism that eats **producers** (the second trophic level).

A **carnivore** that eats **primary consumers** (the third trophic level).

A **carnivore** that eats **secondary consumers** (the fourth trophic level).

**Count the arrows from the producer** up to it: 1 producer, 2 primary, 3 secondary, 4 tertiary consumer.

**Yes** — in a food web an organism that feeds at different levels (e.g. eats both a herbivore and a carnivore) occupies two levels at once.

**Trace its arrows backwards** until you reach a **producer**, which originally captured the energy from **sunlight**.

**Sunlight** — captured by producers during **photosynthesis**.

About **10%** — the other ~90% is lost at each level.

As **heat from respiration**, in **faeces (undigested waste)**, and in **uneaten or dead material**.

**Heat from respiration** — it leaves the ecosystem and cannot be passed on as food.

The **percentage** of energy at one trophic level that is passed on to the next — usually about **10%**.

A diagram in which each bar shows the **energy** at one trophic level; the bars **get smaller** up the levels because energy is lost at each step.

Because each level holds **less energy** than the one below — only ~10% is passed on each step.

**No** — energy flows **one way** (sunlight → producers → consumers) and is steadily **lost as heat**; only nutrients are recycled.

After several transfers **too little energy remains** to support another trophic level.

As **sunlight**, trapped by producers through **photosynthesis**.

Only the energy built into its **biomass (body)** — and only the part that is actually **eaten**.

Energy is lost at each trophic level, so the **extra transfer** (and cattle's poorer feed conversion) wastes more energy.

There is **very little energy** left at the top trophic level, so it can only support **a small number** of them.

A pollutant that is **not broken down** by enzymes or decomposers, so it stays in the environment and in organisms for a long time (e.g. DDT, mercury).

The **build-up of a pollutant inside a single organism** over time, because it is taken in faster than it can be broken down or excreted.

The **increase in a pollutant's concentration from one trophic level to the next**, so that it is highest in the top predator.

It is **persistent (non-biodegradable)** and **not excreted** — so it is stored (often in fat) and passed on.

Each consumer eats **many** contaminated prey and **stores all** their pollutant, so the concentration **multiplies at each trophic level**.

It **increases** up the chain — the opposite of energy, which decreases.

The pollutant is **stored and passed on** (not used up or lost), whereas energy is lost as heat at each level.

**DDT** (a pesticide) or **methyl mercury** — both are persistent and stored, not excreted.

It biomagnified to high levels and caused **thin eggshells**, reducing breeding success and causing **population decline**.

In **fat (fatty tissue)**, because they are often **fat-soluble** — so they are not excreted.

Bioaccumulation is **within one organism**; biomagnification is **between trophic levels** (up the chain).

It names the process but does not give the **cause-and-effect** — you must say it is stored and that each consumer eats many prey, so it multiplies up the chain.

The continuous **recycling of carbon** between the atmosphere, living organisms, the oceans and rocks — carbon is never made or destroyed.

**Photosynthesis** — producers fix CO₂ into organic carbon (glucose).

**Respiration, decomposition and combustion.**

By **feeding** — organic carbon passes along the **food chain**.

**All living things** — producers, consumers and decomposers — releasing CO₂.

Decomposers (bacteria, fungi) break down dead matter and **respire**, releasing the stored carbon as **CO₂**.

The **burning** of wood and fossil fuels, which releases their stored carbon as **CO₂**.

From **dissolved CO₂ and hydrogencarbonate (HCO₃⁻) ions** in the water around them.

As **CO₂ gas** taken directly from the air.

A store that **takes carbon out of the air** — e.g. forests, peat bogs, limestone, fossil fuels, the deep ocean.

Something that **releases CO₂ into the air** — respiration, decomposition and combustion.

**Waterlogged, anaerobic (low-oxygen) and acidic** conditions slow decomposition, so carbon-rich material builds up.

When **combustion of fossil fuels** (a source) adds CO₂ **faster than photosynthesis** (the sink) can remove it.

The **photosynthesis** arrow — running from CO₂ in the air into living things.

An organism that feeds on **dead organic matter** and breaks it down, **releasing nutrients** back to the environment.

**Detritivores** and **saprotrophs**.

A decomposer (mostly **bacteria and fungi**) that **secretes enzymes onto** dead matter and **absorbs** the soluble products — it digests **externally**.

An **animal** (e.g. earthworm, woodlouse) that **ingests** pieces of dead matter and digests them **internally**, in a gut.

**Where digestion happens**: a detritivore digests **internally** (it ingests); a saprotroph digests **externally** (it secretes enzymes and absorbs).

Both are **decomposers** — they feed on **dead organic matter** and **recycle nutrients** back to the environment.

They **break down dead organic matter** AND **release/recycle inorganic nutrients** to the soil for producers to reuse.

The repeated movement of nutrients (carbon, nitrogen, phosphorus) **between living organisms and the environment**, so the same atoms are **reused**.

They **unlock the nutrients** trapped in dead matter; without them, nutrients would stay locked away and **producers would run out of raw materials**.

**Boxes = stores** of nutrients (soil, litter, biomass); **arrows = transfers** of nutrients between the stores.

**Uptake by plant roots** and **leaching** (nutrients washed out by water); also runoff/erosion.

It is **warm and wet**, so **decomposers are very active** and break litter down **quickly**, releasing nutrients fast.