Topic 6 - Plant Structures and Their Functions

Question 1

What is photosynthesis?

Answer 1

A process in which an organism uses energy from the sun to make glucose.

Question 2

What are photosynthetic organisms?

Answer 2

An organism that uses photosynthesis to create food. These are mainly plants

Question 3

What is the glucose formed by photosynthesis used for?

Answer 3

To feed the plant and to form larger molecules that allow the plant to grow.

Question 4

What is biomass?

Answer 4

The mass of living material in an organism.

Question 5

Where in the cell does photosynthesis occur?

Answer 5

In the chloroplast.

Question 6

What is a chloroplast?

Answer 6

A subcellular structure that houses the reactions for photosynthesis in its chlorophyll.

Question 7

What is chlorophyll?

Answer 7

A green substance found in chloroplasts that allows photosynthesis to occur.

Question 8

How does photosynthesis occur?

Answer 8

Energy from sunlight is absorbed by the chlorophyll which gives the reaction the necessary energy to occur.

Question 9

What is the photosynthesis reaction?

Answer 9

Carbon Dioxide + Water →(Light)→ Glucose + Oxygen

6CO₂ + 6H₂O →(Light)→ C₆H₁₂O₆ + 6O₂

Question 10

What type of reaction is photosynthesis? Why?

Answer 10

Endothermic, because energy is taken in during the reaction.

Question 11

How does the light level affect photosynthesis?

Answer 11

Provided there are no other limiting factors, the more light there is, the faster the rate of photosynthesis.

Question 12

Describe the relation between light intensity and distance. How is it written in an equation?

Answer 12

Light intensity is inversely proportional to the square of the distance.
Light intensity ∝ 1÷Distance²

Question 13

How does the CO₂ concentration affect photosynthesis?

Answer 13

Provided there are no other limiting factors, the higher the CO₂ concentration, the faster the rate of photosynthesis.

Question 14

How does the temperature affect photosynthesis?

Answer 14

Lower temperatures slow down the reaction, however, if raised above a certain temperature the reaction will slow down again before stopping completely due to the enzymes in the reaction becoming denatured and useless. This normally happens around 45°C.

Question 15

What are root hair cells? Describe them and what do they do.

Answer 15

Cells that grow on the surface of plant roots, they have a hair-like extension which gives them a large surface area. They take in water and mineral ions from the soil.

Question 16

How do plants take in water? Why is this method used?

Answer 16

Osmosis into the roots, because there is often a lower concentration of water in the root than in the soil.

Question 17

How do plants take in mineral ions? Why is this method used?

Answer 17

Active transport into the roots, since there is often a higher concentration of mineral ions in the root than in the soil.

Question 18

What are phloem tubes?

Answer 18

Tubes found in plants made from elongated living cells with small pores in their end walls these cells are called phloem.

Question 19

What do phloem tubes do?

Answer 19

They transport food substances from the leaves to the rest of the plant for use or storage, this is called translocation, which requires energy, and goes in both directions.

Question 20

What are xylem tubes?

Answer 20

Tubes found in plants made from elongated dead cells joined end to end with no end walls, these cells are called xylem.

Question 21

What do xylem tubes do?

Answer 21

They transport water and mineral ions from the roots to the stem and leaves, using transpiration, which requires no energy but only goes in one direction.

Question 22

How do xylem tubes maintain their structure?

Answer 22

Before they die, they strengthen their walls with a substance called lignin.

Question 23

What is transpiration?

Answer 23

The movement of water in a plant.

Question 24

What causes transpiration?

Answer 24

Water evaporates and diffuses out of the plant, this causes a lower concentration of water in the plant than in the soil, which causes water to enter the roots by osmosis.

Question 25

What are stomata?

Answer 25

Tiny pores on the surface of a plant, most commonly found on the underside of leaves.

Question 26

What is the purpose of stomata?

Answer 26

To allow Carbon Dioxide and Oxygen to diffuse in and out of the leaf.

Question 27

Why does water escape the plant from the leaves?

Answer 27

The higher concentration of water in the leaf means that when the stomata are open the water diffuses out.

Question 28

Describe the structure of stomata?

Answer 28

A gap between two guard cells, that change shape to control the size of the stoma.

Question 29

How do guard cells work?

Answer 29

When the guard cells swell with water (become turgid) they become rigid and create a larger opening between them.
When the guard cells lose water (become flaccid) they become limp and create a smaller opening.

Question 30

How does light intensity affect the rate of transpiration? Why is this?

Answer 30

The brighter it is, the faster the rate of transpiration. This is because the stomata close as it gets darker since photosynthesis cannot occur in the dark, so there is no need to be open, which prevents water from escaping the plant.

Question 31

How does temperature affect the rate of transpiration? Why is this?

Answer 31

The warmer it is, the faster the rate of transpiration. This is because the water particles have more energy and more evaporation occurs, so more water vapour diffuses out in transpiration.

Question 32

How does air flow affect the rate of transpiration? Why is this?

Answer 32

The more air flow there is, the faster the rate of transpiration. This is because the water vapour that diffuses out of the plant is blown away quickly, so the concentration gradient between the plant and air remains high so diffusion continues.

Question 33

How is the rate of transpiration estimated?

Answer 33

Using a potometer it is possible to measure the amount of water taken up by a plant based off of the distance moved by a bubble of air through a capillary tube full of water over time taken.

Question 34

What are layers of a leaf from the top down?

Answer 34

Waxy cuticle
Upper epidermis
Palisade mesophyll
Sponge mesophyll
Lower epidermis

Question 35

How is a leaf’s shape adapted to its purpose?

Answer 35

It is wide to increase surface area, so it absorbs more light which is needed for photosynthesis.

Question 36

How is the palisade layer adapted to its purpose?

Answer 36

It has a lot of chloroplasts, and it is near the top of the leaf to absorb more light, which is needed for photosynthesis.

Question 37

How is the upper epidermis adapted for its purpose?

Answer 37

It is transparent so light can reach the palisade layer.

Question 38

How is the position of the xylem and phloem an adaptation of leaves?

Answer 38

The network of vascular bundles which provides the leaf with water, remove the glucose produced and maintain the leaf’s structure.

Question 39

How is the waxy cuticle an adaptation of leaves?

Answer 39

It seals the leaf which prevents unnecessary water loss by evaporation.

Question 40

How is the lower epidermis adapted to its purpose?

Answer 40

It contains the stomata which allows CO₂ diffuse directly into the leaf.

Question 41

How is the spongy mesophyll adapted to its purpose?

Answer 41

It contains air spaces which increase the rate of diffusion of gasses in and out of the leaf’s cells.

Question 42

How are some plant’s leaves adapted to more extreme climates? Why is this?

Answer 42

Small leaves/ spines: reduces the surface area so less water is lost through evaporation, spines also help to stop animals eating the plant for water.
Curled leaves/ hairs on the leaves: reduces the air flow close to the leaf, trapping water vapour near the stomata, which slows the rate of diffusion.
Thick waxy cuticle: Blocks more heat so there’s less water lost by evaporation.
Fewer stomata/ stomata that open only at night: Less water is lost by evaporation
Stomata sunken in pits: Reduces air flow close to the stomata which slows the rate of diffusion.

Question 43

What are auxins?

Answer 43

Plant hormones that control the cell elongation process to control the direction the plant grows in.

Question 44

Where are auxins produced?

Answer 44

In the meristems at the tips of the shoots and roots.

Question 45

How do auxins work in shoots?

Answer 45

They diffuse backwards from the meristem accumulating in the cells with the least light and the cells which are lowest, where they promote cell elongation, causing the tip to curve towards the light and away from the direction of gravity.

Question 46

What is phototropism? What does it mean for a part of a plant to be positively or negatively phototropic?

Answer 46

A growth response to light. Positive phototropism means that the part of the plant grows towards a light source, whereas, negative phototropism is where the part of the plant grows away from a light source.

Question 47

What is gravitropism? What does it mean for a part of a plant to be positively or negatively gravitropic?

Answer 47

A growth response to gravity. Positive gravitropism means that the part of the plant grows towards the direction of gravity, whereas, negative gravitropism is where the part of the plant grows against the direction gravity.

Question 48

How do auxins work in roots?

Answer 48

The auxins diffuse backwards from the meristem accumulating in the cells with the least light and the cells which are lowest, where they inhibit cell elongation, causing the tip to curve away from the light and towards the direction of gravity.

Question 49

How would the growth responses of shoots be described?

Answer 49

Positively phototropic and negatively gravitropic.

Question 50

How would the growth responses of roots be described?

Answer 50

Positively gravitropic and negatively phototropic.

Question 51

How are plant hormones used as selective weedkillers?

Answer 51

Most weeds growing in crop fields or lawns are broad-leaved, whereas, grasses and cereals are narrow-leaved. Selective weedkillers use auxins which only affect broad-leaved plants. This disrupts the weed’s normal growth patterns which quickly kills them whilst leaving the grass and crops untouched.

Question 52

How are plant hormones used in rooting powders?

Answer 52

A cutting is a part of a plant that has been cut off. On their own, they normally wouldn’t grow, however, if rooting powder which contains auxins is added, they will produce roots and grow normally as new plants. This allows for the rapid cloning of good plants.

Question 53

What are gibberellins?

Answer 53

Plant hormones that stimulate seed germination, stem growth and flowering.

Question 54

How are plant hormones used to control fruit and flower production in plants?

Answer 54

Plants can be given gibberellins to cause them to slower earlier than normal or in conditions that they normally wouldn’t, so fruit can be produced year round.
Similarly, they can be used to reduce the number of flowers produced per plant, so the fruits don’t have to compete over resources, so the fruit quality is improved.

Question 55

How are plant hormones used to produce seedless fruit?

Answer 55

Plants normally have to be pollinated to produce fruit, however, if some types of plant’s unpollinated flowers are given gibberellins, the flower will bear fruit without seeds.

Question 56

What is ethene?

Answer 56

A plant hormone that controls fruit ripening.

Question 57

How are plant hormones used to control fruit ripening?

Answer 57

The fruits are picked whilst unripe and less easily damaged, then during transportation, they are given ethene which causes them to ripen so that they will be perfectly ripe at the shop.

Question 58

How are plant hormones used to control seed germination?

Answer 58

Seeds can be treated with gibberellins, which causes them to germinate at times they normally wouldn’t, this is used to make sure the plants can grow year round and each batch germinates around the same time.