Biology - Unit 6: Plant Nutrition

what is photosynthesis?

the process by which plants make carbohydrates from raw materials using energy from light

what is chlorophyll?

a green pigment that is found in chloroplasts

what does chlorophyll do?

transfer light energy into chemical energy for the formation of glucose and other carbohydrates

what is the use of starch?

energy store

what is the use of cellulose?

build cell walls

what is the use of glucose?

used in respiration to provide energy

what is the use of sucrose?

transport through the plant

state the word equation for photosynthesis

carbon dioxide + water → glucose + oxygen

(in the presence of light and chlorophyll)

state the balanced chemical equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

(in the presence of light and chlorophyll)

how does light intensity affect the rate of photosynthesis?

as light intensity increases, the rate of photosynthesis will also increase as photosynthesis is a chemical reaction that requires light energy, so when less light energy is available, the reaction occurs at a reduced rate

how does CO₂ concentration affect the rate of photosynthesis?

as CO₂ concentration increases, so does the rate of photosynthesis as CO₂ is a reactant in photosynthesis, so reducing its availability will reduce the rate at which the reaction can proceed

how does temperature affect the rate of photosynthesis?

• photosynthesis is controlled by enzymes, so temperature affects its rate.

• as temperature rises, photosynthesis increases because molecules have more kinetic energy and collide more often.

• beyond the optimum temperature, the rate decreases and can stop.

• extremely high temperatures denature enzymes, stopping photosynthesis completely.

state the 3 main factors that limit the rate of photosynthesis

• temperature

• CO₂ concentration

• light intensity

what features do most leaves have and how are they adaptations for photosynthesis?

• large surface area to maximise light absorption

• thin to allow efficient movement of gases between leaf cells and the surrounding air

label the diagram

A - waxy cuticle

B - vascular bundle

C - upper epidermis

D - palisade mesophyll

E - spongy mesophyll

F - lower epidermis

G - air spaces

H - stomata

I - guard cells

what is a limiting factor?

an environmental factor that limits the rate of a reaction

how is the waxy cuticle an adaptation of photosynthesis?

protects the leaf and reduces water loss by evaporation while allowing light through

how is the stomata an adaptation of photosynthesis?

allow CO₂ to diffuse into the leaf, and oxygen and water vapour to diffuse out

how are guard cells an adaptation of photosynthesis?

plants can close the stomata to reduce water loss

how is the spongy mesophyll an adaptation of photosynthesis?

carry out photosynthesis, and allow the easy movement of gases

how is the palisade mesophyll an adaptation of photosynthesis?

many cells can fit in a single layer beneath the upper surface of leaves, maximising photosynthesis

how is the vascular bundle an adaptation of photosynthesis?

allows the raw materials of photosynthesis to reach the leaf

how is the xylem an adaptation of photosynthesis?

provides water for photosynthesis, and maintains the transpiration stream

how is the phloem an adaptation of photosynthesis?

allows the products of photosynthesis to travel away from the leaves to other parts of the plant

how is the upper epidermis an adaptation of photosynthesis?

allows light to pass through to the palisade and spongy mesophyll cells

how is the lower epidermis an adaptation of photosynthesis?

allows gas exchange to take place

what is the importance of nitrates in plants?

nitrates are needed to build amino acids, which forms proteins. lack of nitrates leads to inability to produce amino acids and build proteins, so they will have reduced growth

what is the importance of magnesium in plants?

chlorophyll production. lack of magnesium leads to plants appearing yellow and reduced growth due to reduced photosynthesis

how can we investigate the need for chlorophyll for photosynthesis?

1. find a plant with leaves with green parts and non-green parts

2. keep the plant in the dark for 48 hours and then test both the green and non-green parts for starch

3. move the plants into sunlight and then wait another 48 hours and test both parts of the plant again

4. the green parts containing chlorophyll and these should be the only ones testing positive for starch in the second test

how can we investigate the need for light for photosynthesis?

1. put a plant in the dark for 48 hours

2. remove the plant and place a strip of opaque tape over part of a leaf

3. leave the plant in the sun for 48 hours

4. remove the tape and test the part of the plant that didn’t have the tape on and also the part that didn’t have the tape on for starch and compare the results

5. the uncovered section should be the only one that tests positive for starch

how can we investigate the need for CO₂ for photosynthesis?

1. place transparent plastic bags over 2 separate plants

2. place sodium hydrogencarbonate inside the bag of one plant (produces CO₂₎

3. place soda lime in the other (absorbs CO₂₎

4. test the plant leaves for starch a day later

5. the leaves from the sodium hydrogencarbonate plant should only test positive for starch

how can we investigate the rate of photosynthesis?

1. to investigate how fast photosynthesis is happening use an aquatic plant that photosynthesises in water and count the number of oxygen bubbles it releases in a minute

2. as photosynthesis occurs, oxygen gas is made and released

3. since the plant is in water, the oxygen released can be seen as bubbles leaving the plant

4. the number of bubbles produced over a minute can be counted to record the rate

5. the more bubbles produced per minute, the faster the rate of photosynthesis

• to change the light intensity, move the lamp to different distances away from the beaker containing the plant

• to change the CO₂ concentration, different amounts of sodium hydrogencarbonate may be dissolved in the water in the beaker

• to change the temperature, change the temperature of the water in the beakers to different levels