SB6

Question 1

How do plants make their own food?

Answer 1

Photosynthesis.

Question 2

What’s happens during photosynthesis?

Answer 2

1. Photosynthesis organisms, such as green plants and algae, use energy from the sun to make glucose.
2. Some is used to make larger, complex molecules that the plants or algae need to grow.
   These make up the organisms biomass.
3. The energy stored in the organisms biomass then works its way through the food chain as animals eat them and each other.
   So photosynthetic organisms are the main producers of food for nearly all life on earth.

Question 3

What is some of the glucose used for in photosynthesis?

Answer 3

Some is used to make larger, complex molecules that the plants or algae need to grow.
These make up the organisms biomass.

Question 4

What is biomass?

Answer 4

The mass of living material.

Question 5

What happens to the energy stored in organisms biomass?(photosynthesis)

Answer 5

The energy stored in the organisms biomass then works its way through the food chain as animals eat them and each other.
So photosynthetic organisms are the main producers of food for nearly all life on earth.

Question 6

Where does photosynthesis occur?

Answer 6

It happens inside chloroplast - they contain chlorophyll which absorbs light.
Energy is transferred to the chloroplast by light.

Question 7

What’s the equation for photosynthesis?

Answer 7

Carbon dioxide + water = (light)(chlorophyll) = Glucose + oxygen

Question 8

What type of reaction is photosynthesis?

Answer 8

It’s an endothermic reaction - energy is taken in during the reaction.

Question 9

What affects the rate of photosynthesis?

Answer 9

1. Light intensity.
2. Concentration of carbon dioxide.
3. Temperature.

Any of these can become the limiting factor

Question 10

What’s meant by the limiting factor?

Answer 10

It’s stopping something (photosynthesis) from happening any faster.

Question 11

What happens to the rate if there’s not enough light?

Answer 11

It slows down.

Question 12

Explain how light affects the rate of photosynthesis?

Answer 12

1. Light transfers the energy needed for photosynthesis.
2. At first, as the light level is raised, the rate of photosynthesis increases steadily (the rate is directly proportional to light intensity). But this is only up to a certain point.
3. Beyond that, it wont make any difference - it’ll be either the temperature or the CO2 level which is the limiting factor.

Question 13

Explain how CO2 affects the rate of photosynthesis?

Answer 13

1. CO2 is one of the raw materials needed for photosynthesis.
2. Increasing the CO2 concentration increases the rate of photosynthesis up to a point. After this it flattens out, showing that its no longer the limiting factor.
3. As long as light an CO2 are in plentiful supply then the factor limiting photosynthesis must be temperature.

Question 14

What happens to the rate if there’s not enough CO2?

Answer 14

It slows down.

Question 15

Explain how temperature affects the rate of photosynthesis?

Answer 15

1. Usually, if the temperature is the limiting factor it’s because its too low - the enzymes needed for photosynthesis work more slowly at a low temperature.
2. But if the plant gets too hot, the enzymes it needs for photosynthesis and its other reactions will be denatured.
3. This happens at about 45 degrees C.

Question 16

What do root hair do?

Answer 16

They take in minerals and water.

Question 17

Explain how root hairs take in minerals and water?

Answer 17

1. The cells on the surface of plants roots grow into ‘hairs’, which stick out into the soil.
2. Each branch of a root will be covered in millions of these microscopic hairs.
3. This gives the plant a large surface area fro absorbing water and mineral ions from the soil.
4. The concentration of mineral ions is usually higher in the root hair cells than in the soil around them, so mineral ions are absorbed by active transport, where as water is absorbed by osmosis.

Question 18

What do phloem tubes transport?

Answer 18

Food

Question 19

Explain how phloem tubes transport food?

Answer 19

1. Phloem tubes are made of columns of elongated living cells with small pores in the end walls to allow stuff to flow through.
2. They transport food substances (mainly sucrose) made in the leaves to the rest of the plant fro immediate use or for storage.
3. This process is called translocation and it requires energy from respiration. The transport goes in both directions.

Question 20

What do xylem tubes carry?

Answer 20

They take up water.

They also carry water and mineral ions, from the roots to the stem and leaves.

Question 21

Explain what xylem tubes are made of and do?

Answer 21

1. They’re made of dead cells joined end to end with no end walls between them and a hole down the middle.
   They’re strengthened with a material called lignin.
2. They carry water and mineral ions from the roots to the stem a leaves.
3. The movement of water from the roots, through the xylem and out of the leaves is called the transpiration stream.

Question 22

What is a transpiration stream?

Answer 22

The movement of water from the roots, through the xylem and out of the leaves.

Question 23

What is transpiration?

Answer 23

The loss of water from the plant.

Question 24

Explain water happens in transpiration?

Answer 24

1. It’s caused by evaporation and diffusion of water from a plants surface. Most transpiration occurs at the leaves.
2. The loss of water creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it.
3. This in turn means more water is drawn up from the roots, and so there’s a constant transpiration stream of water through the plant.
4. The transpiration stream carries mineral ions that are dissolved in the water along with it.

Question 25

What are stomata needed for?

Answer 25

Gas exchange.

They allow CO2 and oxygen to diffuse directly in and out of a leaf, they also allow water vapour to escape during transpiration.

Question 26

What are stomata?

Answer 26

They’re tiny pores on the surface of a plant. They’re mostly found on the lower surface of leaves.

Question 27

Explain what guard cells do?

Answer 27

Stomata are surrounded by guard cells, which change shape to control the size of the pore.

When guard cells are turgid (swollen with water) the stomata opens.

When guard cells are flaccid (low on water and limp) the stomata are closed.

Question 28

What environmental factors affect transpiration rate?

Answer 28

1. Light intensity
2. Temperature
3. Air flow

Question 29

Explain how light intensity affects the rate of transpiration

Answer 29

The brighter the light the greater the transpiration rate.

Stomata begin to close as it gets darker photosynthesis cant happen in the dark, so they don’t need to open to let CO2 in. When stomata are closed very little water can escape.

Question 30

Explain how temperature affects the rate of transpiration

Answer 30

The warmer it is, the faster transpiration happens.

When it’s warmer the water particles have more energy to evaporate and diffuse out of the stomata.

Question 31

Explain how air flow affects the rate of transpiration

Answer 31

The better the air flow around a leaf (strong winds), the greater the transpiration rate.

If air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away. This means there’s a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn’t happen as quickly.

If there’s good air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly, from an area of higher concentration to an area of lower concentration.

Question 32

What’s the equation to estimate transpiration rate?

Answer 32

Transpiration rate = Distance moved / time taken

Question 33

How are leaves adapted for photosynthesis and gas exchange?

Answer 33

1. Leaves are broad, so there’s a large surface area exposed to light.
2. The palisade layer ha lots of chloroplast. This means that they’re near the top of the leaf where they can get the most light.
3. The upper epidermis is transparent so that light can pass through it to the palisade layer.
4. The xylem and phloem form a network of vascular bundles, which provide the leaf with water for photosynthesis and take away the glucose produced. They also support the structure.
5. The epidermal tissues are covered with a waxy cuticle, which helps to reduce water loss by evaporation.
6. The tissues of leaves are also adapted for efficient gas exchange (the lower epidermis has lots of stomata, which let CO2 diffuse directly into the leaf). Also, the spongy mesophyll tissue contains air spaces which increase the rate of diffusion of gases into and out of the leafs cells.

Question 34

Describe how some plants are adapted to live in extreme conditions.

Answer 34

1. Small leaves, or spines instead of leaves - this reduces the surface area for water loss by exportation. Spines also help protect it from animas.
2. Curled leaves, or hairs on the surface of leaves - this reduces air flow close to the leaf, trapping water vapour near the surface and reducing diffusion from the leaf to the air.
3. Thick waxy cuticles - again to reduce water loss by evaporation.
4. A thick, fleshy stem, which stores water
5. Fewer stomata or stomata that only open at night - to reduce water loss by evaporation.

Question 35

Name three plant hormones

Answer 35

1. Auxins
2. Gibberellins
3. Ethene

Question 36

Explain what auxins are and do?

Answer 36

1. They’re plant hormones which control growth at the tips of shoots and roots. They move through the plant in solutions (dissolved in water).
2. Auxin is produced in the tips and diffuses backwards to stimulate the cells elongation process which occurs in the cells just behind the tips.
3. Auxin promotes growth in the shoot, but actually inhibits growth in the root.
4. Auxins are involved in the growth responses of plants to light (phototropism) and gravity (gravitropism).

Question 37

What’s phototropism?

Answer 37

Phototropism is the growth of an organism which responds to a light stimulus

Question 38

Explain how shoots are positively phototropic

Answer 38

1. Grow towards light.
2. When a shoot tip is exposed to light, it accumulates more auxin on the side that’s in the shade than the side that’s in the light.
3. This makes the cells grow faster (elongate) on the shaded side, so the shoot bends towards the light.

By bending towards the light, the shoot will be able to absorb more light for photosynthesis, which enables the plant to grow.
Shoots growing completely in the dark will be tall and spindly because the auxin in the tips makes them elongate quickly on all sides. A taller shoot has a better chance of finding light.

Question 39

Explain how shoots are negatively gravitropic

Answer 39

1. Grow away from gravity.
2. When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.
3. This causes the lower side to grow faster, bending the shoot upwards.

Question 40

Explain how roots are positively gravitropic

Answer 40

1. Grow towards gravity.
2. A root growing sideways will also have more auxin on its lower side.
3. But in a root the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards.

Question 41

Explain how roots are negatively phototropic

Answer 41

1. Grow away from light
2. If a root starts being exposed to some light, more auxin accumulates on the more shaded side.
3. The auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground

Question 42

What are the commercial uses of plant hormones?

Answer 42

1. Selective weedkillers
2. Growing from cuttings
3. Controlling flower/fruit formation
4. Producing seedless fruit
5. Controlling the ripening of fruits.
6. Controlling seed germination.

Question 43

How are plant hormones used in selective weedkillers?

Answer 43

1. Most weeds growing in fields/gardens are broad-leaved, in contrast to the grasses with narrow leaves.
2. The weedkillers have been developed fro AUXINS, which only affect the broad-leaved plants.
3. They disrupt their normal growth patterns, which soon kills them, leaving the grass and crops untouched.

Question 44

How are plant hormones used for growing with cuttings?

Answer 44

1. A cutting is part of a plant that has been cut off it.
2. Normally, if you stick cuttings in the soil they won’t grow, but if you add rooting powder, which contains AUXINS, they will produce roots rapidly and start growing new plants.
3. This enables growers to produce lots of clones.

Question 45

What are gibberellins?

Answer 45

They are plant hormones that stimulate seed germination, them growth and flowering

Question 46

How are plant hormones used in controlling flower/fruit formation?

Answer 46

1. GIBBERELLINS can also be used to reduce flower formation, which improves fruit quality.
   E.g - apricot trees often produce too many flowers. This causes too many fruits to form - the tree can’t support them all and they grow quite small. Fewer flowers = fewer fruits which are able to grow nice and big.

Question 47

How are plant hormones used in producing seedless fruit?

Answer 47

1. Fruit (with seeds in the middle) normally only grow on flowering plants which have been pollinated by insects. If the flower doesn’t get pollinated, the fruit and seeds don’t grow.
2. If the plant hormones such as GIBBERELLINS are applied to the unpollinated flowers of some types of plant, the fruit will grow but the seeds wont.

Question 48

How are plant hormones used in controlling the ripening of fruits?

Answer 48

1. The ripening of fruits can be controlled either while they are still on the plant, or during transport tot he shops. This allows the fruit to be picked up while its still unripe (firmer = less damage).
2. A ripening hormone called ETHENE is then added and the fruit will ripen on the way to the supermarkets and be perfect just as it reaches the shelves.

Question 49

How are plant hormones used in controlling seed germination?

Answer 49

1. Lots of seeds wont germinate until they have been through certain conditions (e.g - a period of cold or of dryness)
2. Seed can be treated with GIBBERELLINS to make them germinate at times of the year that they wouldn’t normally. It also helps to make sure all seeds in a batch germinate at the same time.