Chapter 5 Nutrition in Plants

Question 1

State and explain the relationship between temperature and photosynthesis. [4] (2011/A6)
(shows a graph of rate/temp)

Answer 1

• When the temperature is low, 1C, rate of photosynthesis is low, 10 arbitrary units, as enzymes are inactive. [1]
• When temperature increases from 10C to 35C, the rate of photosynthesis increases from 10 arbitrary units to 270 arbitrary units because the enzyme molecules gained kinetic energy, increased rate of collision and increased rate of enzyme-substrate complex formation. [1]
• Rate of photosynthesis at 35°C is the highest, at 270 arbitrary units as it is the optimum temperature where the enzymes are most active. [1]
• Fall in the rate of photosynthesis to 0 arbitrary unit as temperature increases beyond optimum, after 35°C to 55°C, as enzyme is denatured. [1]

Question 2

Write the word equation for photosynthesis [1] (2012/A4)

Answer 2

carbon dioxide + water —> glucose + oxygen
(light energy and chlorophyll)

Question 3

State the type of cell where most chloroplasts are found [1] (2012/A4)

Answer 3

Palisade Mesophyll cell

Question 4

Describe the function of the stomata [2] (2012/A4)

Answer 4

Stomata control gaseous exchange between the plant and the environment. They regulate the rate of diffusion [1]
of gases such as oxygen, carbon dioxide and water vapour [1]
in and out of the leaf by opening or closing.

Question 5

Suggest a reason for the position of the palisade cells within the leaf [1] (2017/A2)

Answer 5

For maximum absorption of sunlight

Question 6

Suggest the function of large air spaces in the spongy mesophyll layer of a water lily leaf [1] (2017/A2)

Answer 6

To allow gases to be trapped in the air spaces for gaseous exchange and to provide buoyancy for the leaf to float on the surface of the water.

Question 7

Suggest how the conditions in the greenhouse can be controlled to ensure the maximum growth of plants [5] (2014/B9)

Answer 7

Light – glass walls allow sunlight to enter for photosynthesis to take place.
- Artificial lighting can be used to maximize photosynthesis at night/all the time
Temperature- can be controlled/maintained at 30
– 35 C e.g. heater to ensure optimal rate of photosynthesis
Carbon dioxide – levels can be maintained at
higher than concentration in atmosphere – can
introduce animals into green house or can burn fuels and pass CO2 into greenhouse
Water – pipes can be used to ensure that plants receive supply of water
Minerals – fertilizer can be added to plants or even delivered with the water through pipes to ensure healthy growth of plants

Question 8

Suggest why light is a major factor affecting the growth rate of trees [2] (2016/B8)

Answer 8

Light energy is absorbed by chlorophyll in the green leaves to convert into chemical energy to produce glucose during photosynthesis. [1]
Glucose is oxidised during respiration to release energy for cellular activities and growth

Question 9

State the factors affecting photosynthesis (self)

Answer 9

Light, temperature and amount of carbon dioxide

Question 10

Describe the process of photosynthesis [6] (2018/B10 E)

Answer 10

• Photosynthesis is a process in which light energy is absorbed by chlorophyll and converted into chemical energy.
• It requires inorganic molecules such as carbon dioxide and water for the synthesis of organic molecules such as glucose with oxygen as a byproduct
• Light energy is used to split water molecules into oxygen gas and hydrogen atoms/ ions through photolysis of water;
• During the light independent stage, hydrogen atoms/ ions, chemical energy and enzymes are used to reduce carbon dioxide to glucose;
• Carbon dioxide is obtained through diffusion into the stomata in the leaves and water is obtained from the soil through the roots, up the stem and into the leaves;
• Oxygen, a by-product diffuses out of the leaves via the stomata;
• The chemical equation for photosynthesis is 6CO2 + 6H2O C6H12O6 + 6O2 ;

Question 11

Explain why the rate of photosynthesis is faster on a warm day than on a cold day (2018/B10 E)

Answer 11

• Photosynthesis process is controlled by enzymes
• On a cold day when temperature is lower, enzymes are inactive and enzyme activity is lower, hence rate of photosynthesis is slower;
• Rate of photosynthesis is faster on a warm day with higher temperature as enzymes have more kinetic energy, increasing frequency of effective collisions between enzymes and substrate molecules, increasing rate of formation of enzyme-substrate complexes, increasing enzyme activity;
• Temperature is a limiting factor of photosynthesis;