Plants

Question 1

Upper epidermis

Answer 1

Transparent layer which allows light to pass through to the photosynthetic cells below.

Question 2

Waxy cuticle:

Answer 2

Reduces evaporation of water from the surface of the leaf preventing it from drying out.

Question 3

Lower epidermis:

Answer 3

Tiny pores called stomata
Stomata allow CO2 to enter and oxygen to leave. It also helps to control the amount of water vapour that can pass out of the leaf.

Question 4

Palisade mesophyll:

Answer 4

Consists of palisade cells packed full of chloroplasts, so the chlorophyll can absorb light for photosynthesis.

Question 5

Spongy mesophyll:

Answer 5

Air spaces that allow CO2 to diffuse from the stomata through the spongy mesophyll to the palisade cells. Oxygen has the same process but starts at the palisade cells.

Question 6

Vascular bundle:

Answer 6

Xylem and phloem

Question 7

What is transpiration?

Answer 7

When water is evaporating from the surfaces of leaves.

Question 8

Describe the transpiration stream.

Answer 8

Transpiration starts with the evaporation of water from cells inside the leaf:

The water vapour diffuses through the air spaces in the spongy mesophyll and out of the leaf through the stomata.
Now water passes from the xylem into the leaf to replace the water that has been lost.
Finally, water is drawn into the root hair cells and up the xylem vessels to the leaf.

Question 9

What factors affect the rate of transpiration?

Answer 9

Rate is greater at higher temperatures due to faster evaporation.

Rate is faster in dry conditions as evaporation is faster.

Rate increases in windy conditions:
Wind gets rid of any water vapour, allowing more water to evaporate.

Rate increases when light intensity increases. High light intensity increases the rate of photosynthesis. The stomata now open to allow more CO2 to enter. Water vapour can now pass out of the leaf.

Question 10

How does the stomata work?

Answer 10

Surrounded by two guard cells.
When light intensity is high:
Guard cells swell and change their shape which causes the stomata to open. Now carbon dioxide can diffuse into the leaf and be used in photosynthesis.

Hot conditions:
Stomata closes to reduce water loss by transpiration. That means the plant cannot photosynthesise.

Question 11

Nitrate deficiency in plants

Answer 11

Nitrates are needed to make proteins and promote growth. Lack of this causes stunted growth.

Question 12

Magnesium deficiency in plants

Answer 12

Magnesium ions are needed to create chlorophyll for photosynthesis. Lack of this will make plants suffer from chlorosis and yellowed leaves.

Question 13

How to identify plant disease:

Answer 13

• Gardening manual/website
• Take infected plant to a laboratory so scientists can identify the pathogens.
• Testing kits that identify the pathogen using monoclonal antibodies.

Question 14

Tobacco Mosaic Virus

Answer 14

• viral disease
• causes the leaves to discolour in a mosaic pattern
• the rate of photosynthesis is reduced due to lack of chlorophyll so the growth of the plant is also reduced
• transmitted by contact between plants

Question 15

Rose black spot:

Answer 15

• caused by a fungus
• causes leaves to develop purple/black spots
• leaves often turn yellow and fall off
• causes rate of photosynthesis to fall and reduces growth
• spread by water/wind
• spray plants with fungicides
• remove infected leaves and destroy them

Question 16

Aphids:

Answer 16

Aphids extract nutrients such as sugars from the plant, stunting its growth

• they feed from the phloem
• farmers cultivate ladybird as they eat them

Question 17

Give examples of physical plant defences:

Answer 17

• cellulose cell walls are difficult to penetrate
• leaves are covered by the waxy cuticle which protects plants from attack
• layers of dead cells around stems such as bark which is a barrier to entry by micro-organisms. As bark ages it falls of and is replaced.

Question 18

Give examples of mechanical plant defences:

Answer 18

• sharp thorns protect plant from being eaten by a herbivore
• hairs that irritate the mouths of the herbivore, making it difficult to eat
• leaves which curl or drop when touched to scare herbivores

Mimicry:
White dead nettle looks very similar to stinging nettle but has no sting-less likely to be eaten this way.
Passion flower has bright yellow spots on its leaves that look like butterfly eggs. Stops other butterflies from laying their eggs there.

Question 19

Chemical plant defences:

Answer 19

• release antibacterial chemicals which kill bacteria and prevent them from attacking the plant
• eg. mint and witch hazel
• produce poisons which deter herbivore
  e. g. foxgloves, deadly nightshade, tobacco plants