Plants

Question 1

What is the word and symbol equation for photosynthesis?

Answer 1

Carbon dioxide + water –> Glucose + oxygen

6CO2 + 6H2O –> C6H12O6 + 6O2

Question 2

What is sugar from photosynthesis used for?

Answer 2

Making energy by respiration in cells
Making cellulose for building cell walls
Combining with nitrates to make protein
Making oils for storage in seeds

Question 3

Why are plants important?

Answer 3

They create food, medicine, oxygen and fuel

Question 4

How does light intensity affect the rate of photosynthesis?

Answer 4

As the light level increases, the rate of photosynthesis increases steadily (directly proportional) up go a point, where temperature or CO2 becomes the limiting factor.

Question 5

How do you calculate light intensity?

Answer 5

Light intensity is proportional to 1/distance^2

Question 6

How does carbon dioxide concentration affect the rate of photosynthesis?

Answer 6

Increasing CO2 concentration increases the rate of photosynthesis to a point. After this the graph flattens out as CO2 is no longer the limiting factor.

Question 7

What is the structure of a leaf?

Answer 7

Waxy cuticle - to keep water in the lead
Epidermis - to protect other cells and to give the leaf structure
Palisade cell - contain chloroplasts for photosynthesis
Spongy mesophyll tissue - have gaps between them to let gases move through
Stomata - gaps between guard cells to let gases move in and out of the leaf
Guard cells - can open and close the stomata to allow or prevent gas exchange.

Question 8

What are the three limiting factors of photosynthesis?

Answer 8

Light
Carbon dioxide
Ideal temperature

Question 9

How do plants transport substances?

Answer 9

Water and solutes come from the soil and are absorbed through the roots by osmosis and active transport. Water and solutes then move through the roots until they reach the xylem. They then move up the xylem vessels through the stem to the leaves by transpiration. Water then evaporates through the stomata, known as transpiration.
Sugars, made from photosynthesis, move through the phloem to growing parts of the plant and storage tissues.

Question 10

What are xylem?

Answer 10

Vessels made from dead xylem cells. They transport water and nutrients from the soil. They are one way only and have no end walls between cells. They have thick walls stiffened with lignen.

Question 11

What are phloem?

Answer 11

They are vessels made from living cells. They transport food. The cells have end walls with perforations. They have two way flow.

Question 12

What is the process of transpiration?

Answer 12

Water is collected by the roots through osmosis
As the plant receives sunlight, water evaporates through the stomata
The water that evaporates creates suction, drawing up more water through the xylem to the leaves.

Question 13

What are the factors affecting transpiration?

Answer 13

Light intensity
Wind/ air flow
Humidity
Temperature

Question 14

How does light intensity affect the rate of transpiration?

Answer 14

More water needs to be drawn up to allow the increased rate of photosynthesis, so the stomata open more, increasing the rate of transpiration

Question 15

What is a potometer?

Answer 15

A piece of apparatus that measures water uptake by a plant to measure transpiration rate

Question 16

How does temperature affect the rate of transpiration?

Answer 16

When it is warm particles have more energy to evaporate and diffuse out of the stomata, so transpiration happens faster

Question 17

How does air flow affect the rate of transpiration?

Answer 17

With a good airflow water vapour surrounding the leaf is swept away, so there is a low concentration outside the leaf, so diffusion is quicker, so transpiration is quicker

Question 18

What are auxins?

Answer 18

Plant hormones that control growth at tips of shoots and roots. It is produced in the tips and diffuses backwards to stimulate cell elongation. It promotes growth in the shoot but inhibits growth in the root.

Question 19

What is positive phototropism?

Answer 19

Growing towards light

Question 20

What is positive gravitropism?

Answer 20

Growing towards gravity

Question 21

What is negative phototropism?

Answer 21

Growing away from light

Question 22

What is negative gravitropism?

Answer 22

Growing away from gravity

Question 23

Are shoots positively or negatively phototropic? Why?

Answer 23

Positively, as when it is exposed to light it accumulates more auxin on the side in the shade, making it grow faster on the shaded side, so it bends towards light

Question 24

Are shoots positively or negatively gravitropic? Why?

Answer 24

Negatively, as when it is growing sideways it accumulates more auxin on the lower side from gravity, making it grow faster on the lower side, so it bends upwards

Question 25

Are roots positively or negatively phototropic? Why?

Answer 25

Negatively, as when it is exposed to light it accumulates more auxin on the side in the shade, inhibiting growth on the shaded side, so it bends downwards, back into the ground

Question 26

Are roots positively or negatively gravitropic? Why?

Answer 26

Positively, as when it is growing sideways it accumulates more auxin on the lower side from gravity, inhibiting growth on the lower side, so the root bends downward

Question 27

How can plant hormones be used?

Answer 27

As selective weedkillers, growing from cuttings with rooting powder, controlling flower and fruit formation, producing seedless fruit, controlling ripening of fruits, controlling seed germination.

Question 28

How can plant hormones be used as selective weedkillers?

Answer 28

They are developed from auxins, which only affect broad leaved plants, which are generally weeds. This disrupts normal growth patterns, killing them, while leaving narrow leaved crops alone

Question 29

How can plant hormones be used to grow from cuttings with rooting powder?

Answer 29

A cutting is a cut off part of a plant. Normally they will not grow, but if you add rooting powder, containing auxins, it will produce roots and start growing as a new plant. This is used to clone a good plant

Question 30

How can plant hormones be used to control flower and fruit formation?

Answer 30

Gibberellins stimulate seed germination, stem growth and flowering. They can make plants flower earlier or under different conditions. They can also reduce flower formation, which can improve fruit quality

Question 31

How can plant hormones be used to produce seedless fruit?

Answer 31

Fruit normally only grows on flowering plants that have been germinated. Gibberellins applied to unpollinated flowers can make fruit grow without seeds

Question 32

How can plant hormones control the ripening of fruit?

Answer 32

Fruit can be picked when it is unripe as it is firmer and ripened with ethene on the way to the supermarket

Question 33

How can plant hormones be used to control seed germination?

Answer 33

Lots of seeds will not germinate until they have been through certain conditions. They can be treated with gibberellins to make them germinate at different times of year, and to make all seeds in a batch germinate at the same time

Question 34

How can you investigate the effect of light intensity on the rate of photosynthesis?

Answer 34

Place Canadian pondweed into a container with water. Add sodium hydrogencarbonate to make sure there is enough CO2. Put a source of white light a specific distance away. Leave it for a set amount of time while counting bubbles/ use a gas syringe. Repeat with the light source at different distances.

Question 34

How does temperature affect the rate of photosynthesis?

Answer 34

As temperature increases, the rate of photosynthesis increases too as enzymes work better. However, past a point the enzymes become denatures (at ~45 degrees)

Question 34

What are root hair cells and what do they do?

Answer 34

They are on the surface of plant roots and have a ‘hair’ which sticks out into the soil, giving the plant a large surface area. They absorb water by osmosis and mineral ions by active transport from the soil

Question 35

What are stomata?

Answer 35

Tiny pores on the surface of a plant, usually on the lower surface of leaves. They allow CO2, water vapour and oxygen to diffuse in and out of a leaf

Question 36

What are guard cells?

Answer 36

They surround stomata and change shape to control the size of the pore. When they are turgid the stomata are open and when they are flaccid the stomata are closed.

Question 37

How can you estimate transpiration rate?

Answer 37

Set up a potometer with an air bubble along a capillary tube. As the plant transpires, it takes up water so the bubble moves along. Wait for about an hour and measure how far the bubble has moved.

Question 38

How are leaves adapted for photosynthesis?

Answer 38

Leaves are broad for a large surface area
The upper epidermis is transparent to allow light through
Palisade cells have lots of chloroplasts and are near the top for more light
The spongy mesophyll contains air spaces to increase diffusion rate
Epidermal tissues are covered with a waxy cuticle to reduce water loss

Question 39

How are some plants adapted to live in deserts?

Answer 39

Small leaves or spines to reduce surface area for water loss
Curled leaves or hairs to reduce air flow and trap water vapour
Thick waxy cuticles to reduce evaporation
A thick fleshy stem to store water
Fewer stomata that only open at night
Sunken stomata in pits to reduce air flow

Question 40

How can you investigate plant growth?

Answer 40

Put some cress seeds in a Petri dish lined with moist filter paper. Surround the Petri dish with black card; cut a hole in one side of the card. Shine a light into the box through the hole. Leave the cress seeds for one week and observe the response - they should be growing towards the light.