Plant Structures and their Functions

Question 1

Why are photosynthetic organisms producers of biomass?

Answer 1

Photosynthesis produces glucose, some of which is used to make complex molecules the organism needs to grow, which makes up the organism’s biomass

Question 2

What are some substances produced from glucose?

Answer 2

Glucose is used in respiration and is also used to make starch

Question 3

What is the word equation for photosynthesis?

Answer 3

Carbon dioxide + water> glucose + oxygen
Using light energy
6CO2+6H2O>C6H12O6 + 6O2

Question 4

What happens during photosynthesis?

Answer 4

Carbon dioxide and water are converted to glucose and oxygen using light energy

Question 5

Why is photosynthesis an endothermic reaction?

Answer 5

Light energy is taken in during the reaction and no energy is given out

Question 6

How are a leaf and its cells adapted for photosynthesis?

Answer 6

Leaves are broad so large surface area exposed to light
Palisade layer has lots of chloroplasts so they are near the top of the leaf where there is more light
Upper epidermis transparent so light can pass through to palisade layer
Xylem and phloem form vascular bundles which provide water for photosynthesis and take away glucose produced. They also support the structure
The epidermal tissues have a waxy cuticle, reducing water loss by evaporation.
Lower epidermis has lots of stomata, which let CO2 diffuse directly into the leaf
Spongy mesophyll tissue contains air spaces which increase the rate of diffusion of gases into and out of cells

Question 7

What is a rate of reaction?

Answer 7

A measure of how much the reaction changes over time

Question 8

What is the effect of temperature on the rate of photosynthesis?

Answer 8

Increasing the temperature increases the rate of photosynthesis since enzymes needed for photosynthesis work more slowly at low temperatures. However if the plant gets too hot (about 45 degrees Celsius) enzymes will be denatured

Question 9

What is the effect of carbon dioxide concentration and light intensity on the rate of photosynthesis?

Answer 9

Increasing CO2 concentration increases rate of photosynthesis up to a point, until CO2 is no longer the limiting factor. Light intensity is the same.

Question 10

How are root hair cells adapted to their function?

Answer 10

The cells on the surface of roots grow into hairs which stick out, giving the plant a large surface area.
They have no chloroplasts since they are unnecessary so there is more space
Concentration of mineral ions is higher in root hair cells than in the soil so they are absorbed by active transport.
Water is absorbed by osmosis.

Question 11

How is xylem tissue adapted to its function?

Answer 11

Made of dead cells joined end to end with no end walls between them and a hole down the middle. They are strengthened with lignin.

Question 12

How is phloem tissue adapted to its function?

Answer 12

Phloem tubes are made of columns of elongated living cells with small pores in the end walls to allow food substances (mainly sucrose) to flow through.

Question 13

How does transpiration occur?

Answer 13

Transpiration is caused by the evaporation and diffusion of water from a plant’s surface. Water is drawn up by xylem to replace this, creating the transpiration stream. Water diffuses out of the plant through the stomata.

Question 14

How does translocation occur?

Answer 14

Translocation is the transportation of food substances (mainly sucrose) from the leaves to the rest of the plant using energy from respiration.

Question 15

What is the effect of light intensity on the rate of transpiration?

Answer 15

Brighter the light, higher the rate of transpiration since stomata begin to close as it gets darker.

Question 16

What is the effect of air movement on the rate of transpiration?

Answer 16

More air flow = more transpiration- air flow moves water vapour away from the leaf increasing the concentration gradient.

Question 17

What is the effect of temperature on the rate of transpiration?

Answer 17

The warmer it is, the faster transpiration happens. Warner weather means water particles have more energy to evaporate and diffuse out of the leaf.

Question 18

What is the effect of humidity on the rate of transpiration?

Answer 18

The greater the humidity, the lower the rate of transpiration since the concentration gradient is less steep.

Question 19

How do you measure the rate of transpiration?

Answer 19

Use a potometer. Check revision guide.

Question 20

What are the different tissues in a leaf?

Answer 20

Waxy cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis, xylem, phloem

Question 21

Describe some adaptations plants have in extreme environments.

Answer 21

Small leaves/spines reduce surface area and protect the plant from animals.
Curled leaves/hairy leaves reduce air flow, reducing transpiration
Thick waxy cuticles reduce water loss by transpiration
Thick, fleshy stem stores water
Fewer stomata/stomata only open at night/sunk in pits reduces water loss by transpiration.

Question 22

Name three types of plant hormone.

Answer 22

Auxins
Gibberellins
Ethene

Question 23

What is a tropism?

Answer 23

A stimulus or condition affecting the plant.

Question 24

What does it mean by positive and negative gravi- and phototropism?

Answer 24

A plant which is positively gravitropic grows downwards and one which is negatively phototropic grows away from light and vice versa

Question 25

How do auxins cause positive and negative phototropism in shoots and roots?

Answer 25

Auxin accumulates on the shaded side. In shoots it causes growth so plants bend towards light. In roots it inhibits growth so roots bend away from light.

Question 26

How are auxins used by plant growers?

Answer 26

As selective weedkillers- weeds tend to be broad-leaved, whilst crops tend to be narrow-leaved. Selective weedkillers developed from auxins only affect broadleaved plants, disrupting their normal growth patterns and killing them.
Rooting powder, which contains auxins, causes cuttings to rapidly put down roots and start to grow.

Question 27

How are gibberellins used by plant growers?

Answer 27

To control flower & fruit formation- gibberellins stimulate seed growth, germination and flowering so can be used to make plants flower earlier than usual or under adverse conditions and to reduce flower formation, improving fruit quality and size as fewer fruit are produced. They can also therefore be used to make seeds germinate all year round or to make all seeds in a batch germinate at the same time.
Producing seedless fruit- normally friut only grows from pollinated flowers but if gibberellins are applied to unpollinated flowers of some plants, fruit will grow but seeds won’t.

Question 28

How is fruit artificially ripened using hormones?

Answer 28

Ripening of fruits can be controlled either whilst still on the plant or on the way to the shops, allowing fruit to be picked whilst unripe (and therefore firmer and less easily damaged). The ripening hormone ethene is then added causing fruit to ripen on the way to the supermarket.