Photosynthesis

It **converts light energy into chemical energy** stored in glucose.

The process that **converts light energy into chemical energy** (stored in glucose), using carbon dioxide and water as raw materials.

**Carbon dioxide** and **water**.

**Glucose** and **oxygen**.

**carbon dioxide + water →(light, chlorophyll)→ glucose + oxygen**.

It is the **green pigment** that **absorbs the light energy** used to drive photosynthesis.

In the **bonds of glucose**.

**No** — light is the **energy input**. It is absorbed and converted, but not built into the glucose.

From the **water** that is split during the process.

Photosynthesis needs **light energy**, so it only occurs in the light, releasing **oxygen** as bubbles.

Energy **stored in the bonds of a molecule** (such as glucose); it can be released later by respiration.

**Oxygen (O₂)**.

**Chlorophyll reflects green light** (while absorbing blue and red). The reflected green is what we see.

**Blue** (~450 nm) and **red** (~660 nm).

**Green** (~550 nm) — it is mostly reflected.

A **coloured molecule** that absorbs some wavelengths of light and reflects others; the colour you see is the light it does **not** absorb.

A graph of **how much light a pigment absorbs** at each wavelength (chlorophyll peaks in blue and red, dips in green).

A graph of the **rate of photosynthesis** at each wavelength of light.

Because **only absorbed light can power photosynthesis** — the wavelengths absorbed are the wavelengths that drive it.

Extra pigments (e.g. **carotenoids**) that absorb wavelengths **chlorophyll misses** and pass the energy on to chlorophyll.

They **widen the range of wavelengths** captured, so the plant loses less of the available light energy.

The light the pigment **does NOT absorb** (the reflected light), not the light it absorbs.

That a leaf contains **more than one pigment** — they separate into different **colours** (different Rf values).

About **400 nm (blue/violet)** to **700 nm (red)**, with green near **550 nm**.

**Glucose** (chemical energy) and **oxygen** (a released waste gas).

**Oxygen (O₂)** — a waste product, given off from the splitting of water.

**Carbon dioxide (CO₂)** — a raw material whose carbon is built into glucose.

From the **splitting of water** during the reaction.

The bubbles are **oxygen**, a product of photosynthesis released in the light.

**Oxygen produced** (bubble count / gas volume), **carbon dioxide taken up** (CO₂ indicator), and **pH** of the water.

It changes **colour** with the dissolved carbon dioxide level — as the plant removes CO₂, the colour shifts.

It **removes carbon dioxide**; dissolved CO₂ is acidic, so less CO₂ means **less acid** and a **higher pH**.

**More bubbles per minute** means **more oxygen** is being released, so photosynthesis is **faster**.

How **fast** photosynthesis is happening — e.g. how much **oxygen is produced** (or CO₂ used) each minute.

**Less** acidic — dissolved CO₂ is acidic, so taking it out raises the pH.

Photosynthesis **releases O₂ and absorbs CO₂**; respiration does the opposite (uses O₂, releases CO₂).

The factor in **shortest supply** that holds back the rate of a process. Only raising it can increase the rate.

**Light intensity**, **carbon dioxide concentration** and **temperature**.

Because it is the one in shortest supply; the others are already plentiful, so adding more of them does nothing.

**Light intensity** — while the curve climbs, increasing light increases the rate.

**CO₂ concentration** (or **temperature**) — light is no longer limiting once the rate goes flat.

Because **light is no longer the limiting factor**; another factor (CO₂ or temperature) now limits the rate.

It **plateaus higher up** — more CO₂ lets light keep raising the rate for longer.

It **increases** the rate, because CO₂ is a raw material that was in short supply.

The rate **falls** (and can drop to zero) because the **enzymes denature**.

Photosynthesis uses **enzymes**, and high temperature **denatures** them, destroying their shape so they stop working.

If the curve is **sloping**, the factor on the axis is limiting; if it is **flat**, something else is limiting.

How fast photosynthesis happens — e.g. the volume of oxygen released or CO₂ taken up per minute.

Taking **carbon dioxide (CO₂)** from the air and building its carbon into an **organic molecule** — in plants this happens during **photosynthesis**.

From **carbon dioxide (CO₂)** in the **atmosphere**, fixed during photosynthesis.

**Glucose** — the hub molecule from which everything else is built.

Because the plant **converts** it into all its other molecules: starch, cellulose, amino acids and lipids.

**Respiration** (energy), **starch** (storage), **cellulose** (cell walls), **amino acids / proteins**, and **lipids (oils)**.

Glucose is converted into **glycerol** and **fatty acids**, which are then **joined** (by condensation) to form a **lipid (oil)**.

**Glycerol** and **fatty acids**.

CO₂ is **fixed** in photosynthesis → **glucose** is made → glucose → **glycerol + fatty acids** → these **join** into a **lipid (oil)**, stored in seeds.

**Lipids (oils)** — this is why seeds often store energy as oil rather than starch.

In **seeds**, where their packed energy fuels the growth of the next plant.

**Nitrogen (N)** — taken up from the soil, as well as the carbon from CO₂.

**Starch** — it is built by joining glucose molecules; oils need glucose to be converted to glycerol and fatty acids first.

The **palisade mesophyll** — tall cells packed with chloroplasts near the top of the leaf.

Look for a layer of **tall, column-shaped cells packed with chloroplasts, just below the upper surface**.

A layer of **tall, chloroplast-packed cells** just under the upper surface that does **most of the leaf's photosynthesis**.

A layer of **loosely-packed cells with large air spaces**; the spaces let **CO₂ diffuse** to every photosynthesising cell.

They have **no chloroplasts**, so they are clear and let **light pass through** to the palisade cells below.

To give a **large surface area** for absorbing light (and for gas exchange).

So light and **CO₂ only travel a short distance** to reach the chloroplasts.

**Near the top**, just below the upper epidermis — where the **light is brightest**, so it absorbs the most light.

**Xylem** brings **water** (a raw material); **phloem** carries away the **sugars** made.

**Light** (captured by the broad, transparent-topped leaf), **CO₂** (in through stomata) and **water** (up the xylem).

**Palisade** = tall, packed cells near the **top**; **spongy** = loose, rounded cells with **air spaces lower down**.

The **stomata** (pores controlled by **guard cells**), mainly on the lower surface.