Plants and photosynthesis

Question 1

What affects the rate of photosynthesis?

Answer 1

Light

Question 2

What are free limiting factors for photosynthesis?

Answer 2

• Light intensity
• Carbon dioxide
  -Temperature

Question 3

Why might a plant not photosynthesise at its maximum rate?

Answer 3

Because it may not have unlimited supplies of essential materials like light, carbon dioxide, or water.

Question 4

What happens if a plant has plenty of sunlight, carbon dioxide, water, and a suitable temperature?

Answer 4

The only limiting factor is the plant’s own ability to absorb materials and make them react

Question 5

What is photosynthesis controlled by?

Answer 5

Enzymes

Question 6

Why does the rate of photosynthesis increase with temperature (up to a point)?

Answer 6

Because the kinetic energy of molecules increases, helping enzymes work faster.

Question 7

What happens to photosynthesis above the enzymes’ optimum temperature?

Answer 7

The rate decreases as the enzyme has denatured

Question 8

How does increasing light intensity affect photosynthesis?

Answer 8

It increases the rate up to a point, after which it has no further effect.

Question 9

Why doesn’t increasing light intensity always keep increasing the rate of photosynthesis?

Answer 9

Because chloroplasts can’t absorb any more light beyond a certain point.

Question 10

How does carbon dioxide concentration affect the rate of photosynthesis?

Answer 10

It increases the rate up to about 0.5%, then levels off.

Question 11

Why does the rate of photosynthesis stop increasing after a certain CO₂ concentration?

Answer 11

Because CO₂ is no longer the limiting factor.

Question 12

What are adaptations that help leaves carry out photosynthesis more effectively?

Answer 12

• Large surface area to absorb as much light as possible
• Thin so light can easily reach cells containing a chloroplast
• Short diffusion pathways for gases

Question 13

Why do leaves need effective transport systems?

Answer 13

To transfer the products of photosynthesis to all parts of the plant and to move water and minerals from the root to the leaves

Question 14

What is the function of the cuticle?

Answer 14

• Waxy layer, reduces water loss from the surface of the leaf
• Transparent so light can reach the chloroplasts

Question 15

What is the function of the epidermis?

Answer 15

• Transparent, so light can reach the chloroplasts

Question 16

What is the function of the palisade layer?

Answer 16

• Lots of chloroplasts for photosynthesis

Question 17

What is the function of the spongy layer?

Answer 17

• Air spaces for diffusion of gases
• Contains chloroplasts for photosynthesis

Question 18

What is the function of the stomata?

Answer 18

• Pores that can open and close to regulate transpiration and allow gas exchange

Question 19

Why are the stomata open during the day but closed during the night?

Answer 19

• During the day it is open to allow gas exchange for photosynthesis
• Closed at night to reduce water loss

Question 20

What is the role of the Phloem?

Answer 20

• Transports Sucrose from Photosynthesis to all parts of the plant
• Transport can go up, down, and sideways
• Used for respiration or storage (converted into starch)
• Process is called translocation

Question 21

What is the role of the Xylem?

Answer 21

• Transports water and minerals ions from the roots up to the plant
• Transport is one way only
• Helps support the plant as xylem vessels are thick-walled and rigid

Question 22

Why do plants need water?

Answer 22

• As a reactant in photosynthesis, as minerals are transported from roots to the leaves dissolved in water.
• Water also provides support by filling vacuoles which push against cell walls, keeping it turgid and prevents cells from becoming flaccid.

Question 23

Why are roots required for plants?

Answer 23

As they absorb water through them, the tips of the roots have tiny hair cells that give the root a large surface area to take in more water by osmosis

Question 24

What are soil particles covered in?

Answer 24

A film of soil water as there is a high concentration in the soil water than inside the root hair cells, so water enters the root via osmosis

Question 25

How are mineral salts absorbed by plants and transported to the leaves?

Answer 25

Mineral salts are absorbed as ions by root hair cells through active transport, which requires energy from respiration. Once inside the root hair cells, the ions are carried in solution through the xylem to the leaves.

Question 26

What happens if a plant does not get enough of one or more ions needed?

Answer 26

It will not grow very well, it'll start to show signs of disease due to the lack of mineral ions

Question 27

What does a lack of nitrates cause?

Answer 27

Poor growth

Question 28

What does a deficiency of potassium cause?

Answer 28

Yellowing in the leaf

Question 29

What does a deficiency of phosphate cause?

Answer 29

Poor root growth

Question 30

What do fertilisers contain?

Answer 30

It contains minerals such as nitrogen, phosphorous and potassium which helps plants grow

Question 31

What do fertilisers cause?

Answer 31

The problem of eutrophication where they are washed into rivers and lakes which can kill fish

Question 32

What do fertilisers help do?

Answer 32

Increase crop yields as they make crops grow bigger and faster due to minerals, they must dissolve in water for the plants to absorb them through their roots

Question 33

What is the xylem?

Answer 33

The centre of the root, before water can travel through the plant it must go through the xylem first

Question 34

Why is the layout of the stem of the root structured differently?

Answer 34

The xylem and phloem are arranged differently as they are around the edge of the stem as it forms a vascular bundle

Question 35

How is pressure used in the xylem?

Answer 35

The pressure at the top of the xylem is lowered, while the pressure at the bottom stays high.

Question 36

Why is the pressure at the top of the xylem lowered?

Answer 36

The pressure at the top of the xylem is reduced because of transpiration.

Question 37

Why are the cells being covered in a film of water necessary?

Answer 37

So gas exchange can take place, some of the film of the water evaporates from the cells and diffuses out of the leaf through the stomata

Question 38

What is the transpiration stream and how does it work in plants?

Answer 38

- The transpiration stream is the movement of water from the roots to the leaves through the xylem. - Water is lost from leaf cells and replaced by osmosis from the xylem, creating low pressure at the top. - This pulls more water up, and because water molecules stick together - They move as a continuous column through the xylem.

Question 39

How does temperature effect transpiration?

Answer 39

On a hot day water evaporates quickly from the leaves of a plant. Transpiration increases as temperature increases

Question 40

How does humidity effect transpiration?

Answer 40

As humidity increases, transpiration decreases because the air is already saturated with water vapour, reducing the diffusion gradient between the leaf and the surrounding air.

Question 41

How does wind speed effect transpiration?

Answer 41

The air is saturated with water vapour, reducing the diffusion gradient from the leaf to the air.

Question 42

How does light intensity effect transpiration?

Answer 42

Transpiration decreases as light intensity decreases because stomata close in the dark, preventing water loss.

Question 43

How does surface area effect transpiration?

Answer 43

The more leaves that a shoot has, the larger the surface area, therefore more stomata are present.

Question 44

What can rate of transpiration be determined by?

Answer 44

Measuring the distance travelled by an air bubble along a capillary tube in a set time. A potometer can be used to measure the rate of transpiration under different environmental conditions

Question 45

How does a potometer measure the rate of transpiration?

Answer 45

- A potometer measures transpiration by tracking the movement of an air bubble in a capillary tube. - A leafy shoot is cut and assembled underwater to prevent air bubbles, joints are sealed with Vaseline, and the bubble’s movement over time is recorded. - It’s an indirect measure, assuming water uptake equals water loss.