What is Photosynthesis?
The plant’s process to make energy and nutrients from carbon dioxide and water.
What is the word equation for Photosynthesis?
Carbon Dioxide + Water –> Glucose + Oxygen
Where in a plant does Photosynthesis occur?
What is a plant?
A photosynthetic organism.
What factors limit the rate of photosynthesis?
- Low temperature
- Dim light
- Low carbon-dioxide concentration
Give two examples of specialised plant cells.
Describe the key features inside Phloem cells and their purpose.
- They have sieve tube elements that contain very little cytoplasm so that there is more space to transport sucrose and other nutrients.
- It also contains companion cells which have lots of mitochondria to supply energy from respiration for active transport of sucrose into and out of the sieve tubes.
Describe the key features inside Xylem cells and their purpose.
- They are dead cells so they contain no cytoplasm or cell contents. This allows more space for water containing mineral ions to move through.
- They have holes in their walls called ‘pits’ that allow the water to move out.
- Their walls are strengthened with lignin rings which make them strong and prevent them from collapsing.
- They form a tubular structure.
What is Transpiration?
The loss of water by evaporation from the leaves of a plant.
What is the transpiration stream?
The movement of water from the roots to the leaves is called the transpiration stream.
Describe the Stomata and its location in a plant.
- The Stomata is mainly found in the lower surface of the leaf.
- They contain chloroplast, a nucleus, a vacuole, a cell wall, and a stoma.
What happens when the stoma in the stomata is open and when it is closed?
When the stoma is open, it means water is taken in by the guard cells which causes them to swell and open the stoma.
When the stoma is closed, the guard cells have lost water so they become flaccid and the stoma closes.
What is Translocation?
The transport of sucrose around the plant.
List four adaptations of the leaf.
- Epidermis cells are transparent to let light pass through to the photosynthetic cells.
- The waxy cuticle is transparent to let light through.
- The flattened shape of the leaf gives a large surface area.
- Mesophyll cells are packed with chloroplast for maximum photosynthesis.
- Xylem cells bring water to the cells,
- Phloem cells remove the sugars made by photosynthesis.
- Stomata allow carbon dioxide to enter and oxygen to leave the plant.
- Internal air space increases surface area for diffusion of gases.
What can you use to measure the rate of transpiration?
What is the equation for the rate of transpiration?
Distance moved (by the bubbles) / Time taken
What factors affect transpiration and how?
Light Intensity - High light intensity causes stomata to open which increases the rate of evaporation.
Air movement - Wind blows away moist air from the stomata, which keeps the diffusion rate high.
Temperature - Higher temperature gives the water molecules more energy so they move faster.
What are some adaptations of plants?
- Plants in extremely hot areas have adaptations that prevent more water loss like leaf hairs that trap moist are round the stomata and a waxy cuticle.
- Plants in tropical conditions have large leaves and have stems and leaves that climb up other plants like trees to obtain more light, and ‘drip tips’ so water runs off them.
- Plants in waterlogged soils have spongy tissue in their roots to store oxygen and fine surface roots that take in oxygen at the water surface.
What do plant hormones do?
Control and coordinate plant growth and development.
What is a tropism?
It is a plant’s response to a stimulus by growing.
What is a positive tropism?
When the plant grows towards the stimulus (like sunlight).
What part of the plant shows positive phototropism and why?
The shoots because they grow towards the light.
What part of the plant shows positive gravitropism and why?
The roots because they grow downwards (towards the pull of gravity).
Give three examples of plant hormones.
What do Auxins do?
- They make cells in the plant grow longer.
- They are affected by light and cause phototropism in the shoots.
- Auxins cause cell elongation at the shaded side of the shoot.
Where are auxins used for humans?
In weedkillers and rooting powder.
How are auxins used in weedkillers?
They make unwanted plants grow too fast and die.
What does rooting powder do?
It contains auxins and a small piece of a plant can be grown into new plants by dipping the stalk in the powder and the stalk produces roots quickly.
What do Gibberellins do?
- They stimulate germination of seeds which increases crop yield.
- They stimulate flower and fruit production.
- They stimulate stem elongation (good for crops like sugar cane).
What does Ethene do?
Ripen the fruit or plant.