Nutrition in plants

Question 1

What are the conditions that are essential for photosynthesis?

Answer 1

Sunlight
chlorophyll
carbon dioxide
suitable temperature (enzymes)
water

Question 2

What is photosynthesis?

Answer 2

It is the process by which green plants take in carbon dioxide and water, and in the presence of light [1], to manufacture glucose [1].

Question 3

What is the word equation of photosynthesis?

Answer 3

carbon dioxide + water —–( sunlight + chlorophyll)–> glucose + oxygen

Question 4

Why does photosynthesis require inorganic molecules such as carbon dioxide and water?

Answer 4

It is needed for the synthesis of organic molecules such as glucose.

Question 5

Overall chemical equation of photosynthesis?

Answer 5

6CO2 + 6H2O → C6H12O6 + 6O2

Question 6

Where is glucose stored in plants?

Answer 6

It is stored temporarily as starch in the leaf.

Question 7

What are the factors that control photosynthesis?

Answer 7

Light intensity, carbon dioxide concentration, and temperature.

Question 8

How does light intensity affect the rate of photosynthesis?

Answer 8

The nearer the light source is to the plant, the greater the light intensity that the plant is exposed to.
As light intensity increases, the rate of photosynthesis increases until a certain light intensity is reached.

Question 9

Why is water and chlorophyll not factors of photosynthesis?

Answer 9

The amounts of water and chlorophyll are relatively constant and are unlikely to change throughout the day. Hence they are not the key factors that affect the rate of photosynthesis.

Question 10

When experimenting whether light intensity affects the rate of photosynthesis, what must be kept constant? Describe ways on doing so.

Answer 10

Temperature.
use a water bath to ensure the temperature is kept constant.

CO2 concentration
use a fixed concentration of sodium hydrogen carbonate solution which is a source of carbon dioxide.

Question 11

What is the function of sodium hydrogen carbonate?

Answer 11

It supplies carbon dioxide for the plant to carry out photosynthesis.

Question 12

When will the rate of photosynthesis be maximum?

Answer 12

At light saturation point.

Question 13

Why does rate of photosynthesis remain constant after light saturation point?

Answer 13

This is because after light saturation point, light intensity is no longer the limiting factor. Other factors such as carbon dioxide/ temperature are the factors that would affect the rate of photosynthesis.

Question 14

How do we measure rate of photosynthesis?

Answer 14

1) measure the number of bubbles per unit time
2) measure the volume of oxygen gas produced per unit time

It is assumed that the rate of photosynthesis is directly proportional to the rate of bubbling.

Question 15

Outline briefly, the process of investigating the necessity of light for photosynthesis.

Answer 15

1) destarch plant by placing in dark room
–> prevent photosynthesis ad will use up all the stored starch for metabolism

2) once destarch, cover a part of the leaf with aluminium foil

3) do iodine test, and see the parts that changed blue black under light exposure.

Question 16

What is light compensation point?

Answer 16

It is when the rate of photosynthesis is the same as rate of respiration, at which net gaseous exchange equals 0

Question 17

What is the effect of increasing temperature on the enzymes involved in photosynthesis?

Answer 17

1) photosynthesis controlled by enzymes
2) low temperature = enzymes inactive
3) temperature increase, rate of photosynthesis increase, until optimum temperature reached
4) At extreme temperature higher than optimum temperature, enzymes denatured, rate of photosynthesis decreases drastically/ photosynthesis does not take place

Question 18

Why are experiments needed to repeat a few times?

Answer 18

This is to allow us to obtain an average rate.

Question 19

What is the law of limiting factor?

Answer 19

It is a process influenced by several factors, the rate at which the process proceeds is determined by the factor in the shortest supply.

Question 20

What is the effect carbon dioxide on the rate of photosynthesis?

Answer 20

The higher the concentration of the sodium hydrogen carbonate solution, the greater the volume of carbon dioxide gas supplied to the plant.

As carbon dioxide increases, the rate of photosynthesis increases.

Question 21

Why must we destarch a plant before using i for an experiment?

Answer 21

By doing so, this will ensure that any starch present in the leaves, at the end of experiment, was produced during the experimental procedure.

Question 22

What are the importance of photosynthesis?

Answer 22

1) producers in food chains, they provide energy for organisms through feeding.

2) coals formed from trees provide a source of fuel to release energy

3) removes carbon dioxide from air and releases oxygen. This can purify air constantly and the Earth’s temperature can be maintained. maintaining constant level of oxygen.

Question 23

What happens to glucose in leaves?

Answer 23

1) excess glucose stored as starch in leaves
2) used immediately by plant cells for cellular respiration or to form cellulose cell walls
3) glucose converted into sucrose which is transported to storage organs
4) reacts with nitrates and mineral salts to form amino acids that are combined to form proteins for synthesis of new protoplasm in leaf
5) used to form fats for storage, cellular respiration or synthesis of new protoplasm

Question 24

Why must glucose be broken down during respiration?

Answer 24

This is to release energy for the plant’s use.

Question 25

what are the external structure of the leaf’s?

Answer 25

vein network, lamina and petiole

Question 26

What is the function of the vein network in leaf’s?

Answer 26

1) allows transport of water and dissolved mineral salts to cells in lamina.
2) transport manufactured food form leaves to other parts of the plant

Question 27

What is the function of the petiole?

Answer 27

It positions the lamina for maximum absorption of sunlight and gaseous exchange.

Question 28

What is the function of the lamina?

Answer 28

It has a large surface area to volume ratio to maximise absorption of sunlight.

It allows rapid diffusion of carbon dioxide molecules into the inner cells of the leaf.

Question 29

What are the internal structures of a leaf?

Answer 29

1. upper epidermis
2. mesophyll layer (palisade and spongy mesophyll)
3. lower epidermis (guard cells and stoma)

Question 30

Why is the upper epidermis covered with a waxy layer of cuticle?

Answer 30

It prevents excessive water loss due to evaporation.
Prevents entry of disease causing microbes.

Question 31

Why is the cuticle transparent?

Answer 31

It is o allow sunlight to penetrate to the mesophyll layer for photosynthesis.

Question 32

Describe the palisade mesophyll?

Answer 32

The palisade mesophyll are a few layers of closely packed cells which are long, cylindrical and contain numerous chloroplasts for maximum absorption of sunlight.

Question 33

Describe the spongy mesophyll.

Answer 33

Irregularly shaped cells with numerous large intercellular air spaces.

Question 34

Why is the spongy mesophyll irregularly shaped with numerous large intercellular air spaces?

Answer 34

This is to allow rapid diffusion of gases inside the leaf.

Question 35

Name the order of the internal structures of the leaf with the highest number of chloroplast to the least number of chloroplast.

Answer 35

palisade mesophyll > spongy mesophyll > guard cells

Question 36

Why is the palisade mesophyll layer long and cylindrical and packed vertically?

Answer 36

vertical arrangement exposes many cells to light rays.

Question 37

Why is the spongy mesophyll surrounded by a thin film of moisture?

Answer 37

Gases entering the cells can dissolve in the water.

Question 38

describe the vascular bundles of the leaf?

Answer 38

It contains xylem and phloem, allowing for the transport of water and food materials respectively within the plant.

Question 39

What is the function of the guard cells?

Answer 39

It regulates the opening and closing of stomata for diffusion of CO2 and O2 in and out of the leaf.

Question 40

What are the functions of the vascular bundles?

Answer 40

Main purpose: transport
Xylem transports water and dissolved mineral salts to plant cells in the leaf.
Phloem transports manufactured food away from leaf.

Question 41

How does water enter the leaf?

Answer 41

water is transported from the roots to the leaves via the xylem vessels in the veins. [1]

Water leaves the veins and moves from cell to cell in the mesophyll layer by osmosis. [1]

Question 42

How does carbon dioxide enter the leaf?

Answer 42

During the day, process of photosynthesis is actively carried out in the leaf.

concentration of CO2 is lowered due to it being used up rapidly in this process.

Since the concentration of CO2 is higher than the atmosphere, there is a net movement of CO2 molecules diffusing into the leaf by diffusion through the stomata.

CO2 dissolves into the film of moisture surrounding the mesophyll cells and diffuses into cells as a solution.

Question 43

Describe the action of guard cells during the day.

Answer 43

Potassium ions enter guard cells –> conc increase in cells

this results in lower water potential in cells than surrounding.

There is a net movement of water molecules moving into them by osmosis, causing the cells to become turgid and swell

thus opening the stoma.

Question 44

Describe the action of guard cells at night.

Answer 44

Potassium ions leave the guard cells –. conc decreases in cells

this results in higher water potential in cells than in surrounding.

there is a net movement of water molecules out of the cell by osmosis –. causing cells to become flaccid

Thus, stoma closes.