Plants Flashcards
Upper epidermis
Transparent layer which allows light to pass through to the photosynthetic cells below.
Waxy cuticle:
Reduces evaporation of water from the surface of the leaf preventing it from drying out.
Lower epidermis:
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.
Palisade mesophyll:
Consists of palisade cells packed full of chloroplasts, so the chlorophyll can absorb light for photosynthesis.
Spongy mesophyll:
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.
Vascular bundle:
Xylem and phloem
What is transpiration?
When water is evaporating from the surfaces of leaves.
Describe the transpiration stream.
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.
What factors affect the rate of transpiration?
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.
How does the stomata work?
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.
Nitrate deficiency in plants
Nitrates are needed to make proteins and promote growth. Lack of this causes stunted growth.
Magnesium deficiency in plants
Magnesium ions are needed to create chlorophyll for photosynthesis. Lack of this will make plants suffer from chlorosis and yellowed leaves.
How to identify plant disease:
- Gardening manual/website
- Take infected plant to a laboratory so scientists can identify the pathogens.
- Testing kits that identify the pathogen using monoclonal antibodies.
Tobacco Mosaic Virus
- 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
Rose black spot:
- 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
Aphids:
Aphids extract nutrients such as sugars from the plant, stunting its growth
- they feed from the phloem
- farmers cultivate ladybird as they eat them
Give examples of physical plant defences:
- 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.
Give examples of mechanical plant defences:
- 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.
Chemical plant defences:
- 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
