IGSCE Biology - Plant Nutrion, Gas Exhange and Transport

Photosynthesis equation

6CO2 + 6H20 → C6H1206+6O2

Glucose is turned into:

Starch - storage

Sucrose - movement around the plant

cellulose - cell walls

Function of chloroplast

• contains chlorophyll

• Chlorophyll is a green pigment

• It absorbs light energy to make food in the process of photosynthesis

• Chlorophyll traps the energy from the sun and uses it to turn water and carbon dioxide into sugars for the plant

Label the diagram

1. Upper epidermis

2. Mesophyll

3. Lower epidermis

4. Guard cells

5. Wax cuticle

6. Spongy mesophyll

7. Stomata

8. Palisade mesophyll

9. Wax cuticle

How is the leaf adapted for it function?

• the palisade layer is packed full of lots of chloroplast for photosynthesis

• The lead has a transparent upper epidermis to key light through to the palisade layer

• Broad shape to increase surface area to catch more light

• Leaf is thin to allow rapid diffusion for gas exchange

• Air spaces in the spongy mesophyll to allow for gas exchange

• Lots of stomata to allow for gas exchange

• Guard cells control if the stomata is open or closed

• The wax cuticle reduces water loss by evaporation

Factors affecting photosynthesis

1. Light intensity - higher the intensity, faster the rate of photosynthesis.

2. Amount of CO2 - more CO2 = faster rate of photosynthesis

3. Temperature - higher temperature = faster rate of photosynthesis. Temperature affects the enzymes controlling photosynthesis. However, at a certain point the temp. may cause the enzymes to denature

Mineral ions needed by plants

Nitrate ions - contains nitrogen for amino acids and proteins.

Magnesium ions - needed for chlorophyll (leaves green) so they can make glucose.

Practical: testing green leaf for starch

• Leaf in water for 1 min

• Turn off Bunsen burner

• Place leaf into test tube with ethanol for 10 min

• Leaf on petri dish and cover with iodine solution

• The leaf should go black

Practical: how does light effect photosynthesis?

• fill 4 tubes with hydrogencarbonate indicator

• Place pondweed in 2 test tubes

• Cover one pondweed tube with tin foil and one without pondweed with tin foil

• Shine bright light on tubes

  1. Pond weed in light= photosynthesis > respiration = takes up CO2 → alkaline conditions = purple

  2. No pondweed in light=control to show indicator doesn’t change in light

  3. Pondweed in dark=respiration>photosynthesis = lots of CO2 → acidic conditions = yellow

  4. No pondweed in the dark = control

Understand gas exchange in relation to respiration

During the night, oxygen enters the lead and CO2 leaves the leaf. This is to help the leaf respire and because the leaf does not photosynthesise in the night.

Understand gas exchange in relation to photosynthesis

During day, more CO2 enters the leaf than oxygen because, on average, the leaf photosynthesis more than it respires.

Understand how the structure of the leaf is adapted

• leafs are broad → large surface area

• Thin → short distance for gas to travel

• Air spaces in spongy mesophyll → lets gases move easily between cells

• Stomata lets gases like O2 and CO2 in and out the leaf

• Stomata close in the dark to stop CO2 from entering when they cant photosynthesise

Role of stomata

• close in dark to stop CO2 entering

• Open in light to let CO2 enter

• Stomata also close when water supplies from the roots dry up

If CO2 concentration increases, hydrogen-carbonate indicator

Goes from orange to yellow

If CO2 concentration decreases, hydrogen-carbonate indicator

Goes from orange to purple

Phloem

Transports sugars, like sucrose and amino acids from where they’re made, in the leaves, to other parts of the plant

Translocation

The movement of food substances around the plant

Xylem

Carry water and mineral salts from the roots up the shoots to the leaves in the transpiration system

Roots

The cells on the roots grow into long ‘hairs’ which stick out into the soil

There are millions of these ‘hairs’ giving the roots a large surface area for the absorption of water and minerals

Transpiration

• caused by the evaporation and diffusion or water from the plants surface, mostly in the leaf.

• This causes a shortage of water in the leaf, so more water is drawn up from the rest of the plant in the xylem

• This means that more water is drawn up from the roots, and so there is a constant transpiration stream of water throughout the plant

How is the rate of transpiration effected?

Light intensity

• the brighter the light, the greater the rate of transpiration. When stomata are closed, very little water can escape

Temperature

• warmer it is, the faster transpiration happens. Due to energy of water particles increases so diffusing quicker

Wind speed

• higher wind speed = faster rate of transpiration. Due to wind sweeping water vapour away and keeping a low water concentration maintained

Humidity

• drier = faster transpiration. Due to low concentration of water outside the leaf.