Chapter 9 Flashcards
What is a xylem tissue?
It transports water and mineral ions in solution. Move up the plant from the roots to the leaves.
What is the phloem tissue?
It mainly transports sugar both up and down the plant.
How is the xylem adapted for its function?
They are very long, tube-like structures formed from cells joined end to end.
There are no end walls on these cells, making an uninterrupted tube that allows water to pass up through the middle easily.
Cells are dead so no cytoplasm.
Their walls are thickened with a woody substance called lignin, which helps to support the xylem vessels and stops them collapsing inwards. They can be in spirals.
Amount of lignin increase as cells gets older.
Water an ions move into and out of cells through small pits where there’s no lignin.
How is the phloem adapted for function?
Sieve tube elements- They are living cells that form the tube for transporting solutes through the plant.
Joined end to end to form sieve tubes.
Sieve parts have holes in them to allow solutes to pass through.
Sieve tube elements have no nucleus, thin layer of cytoplasm and few organelles.
Companion cells- lack of nucleus and organelles in STE means that it cannot survive on its own so needs companion cell. Provides energy for active transport.
How to dissect plant stems?
Use a scalpel to cut cross section of stem cut thinly- better viewing
Use tweezers to gently place the cut sections in water to stop drying out.
Transfer to dish containing stain- let you see the position in xylem cells.
Rinse of sections with water.
What is the xylem parenchyma?
It contains tannin- bitter chemical- defence against herbivore.
Stores food
What is the symplast pathway?
It goes through the living part of cells- the cytoplasm. The cytoplasms of neighbouring cells connect through plasmodesmata. Water moves through the symplast pathway via osmosis.
What is the apoplast pathway?
It goes through the non living parts of the cells- the cell walls. The walls are very absorbent and water can simply diffuse through them. The water can carry solutes and move from areas of high hydrostatic pressure to areas of low hydrostatic pressure.
What is the casparian strip?
It is in the endodermis .
Blocked by casparian strip which is waxy, made of suberin(impermeable ).
It is waterproof which forces water to move to symplast pathway. This is useful because the cell membranes are partially permeable and are able to control whether substances in water can get through.
Moves to xylem afterwards.
Why is the apoplast pathways the main pathway?
It is because it provides the least resistance.
How is the water moved?
Xylem vessels transport the water all around the plant.
At leaves, water leaves the xylem and moves into the cells by apoplast pathway.
Water evaporates from the cell walls into the spaces between cells in the leaf.
When stomata opens, water diffuses out of leaf into surrounding air.
This is transpiration.
What is transpiration stream?
It is the movement of a column of water up the xylem.
As water is drawn up the xylem, more water is brought into the roots.
This water travels from the roots to the stem via apoplast/symplast pathways.
What is cohesion and tension?
It helps water move up plants, from roots roots to leaves, against the force of gravity.
Tension is when water evaporates from the leaves at the top of the xylem and this creates a tension which pulls more water into the leaf.
Cohesive is when water molecules stick together so when some are pulled into the leaf other follow and means that the whole column of water in the xylem moves upwards.
Water enters the stem through root cortex cells.
What is adhesion?
Attracted to the walls and helps water to rise up xylem vessels.
What is transpiration?
It is the loss of water vapour through the stomata by evaporation.
It causes the plant to wilt, cools the plant down, and causes the transpiration stream.
What factors affect transpiration rate?
Light- the lighter it is the faster the transpiration rate. This s because the stomata open when it gets light, so CO2 can diffuse for photosynthesis. When it’s dark , stomata is closed so little transpiration.
Temperature- higher the temperature the faster the transpiration rate. Warmer water molecules have more energy so evaporate from cells faster. Increases water potential gradient between the inside and outside of leaf, making water diffuse out of leaf faster.
Humidity- lower the humidity , faster the rate of transpiration rate. If the air around the plant is dry, water potential gradient between leaf and air is increased. Increased transpiration.
Wind- the windier the faster the transpiration rate. Lord of air movement blows away water molecules from stomata. Increases water potential gradient, increases rate of transpiration.
Reasons for transpiration stream
Root pressure- minerals moved into xylem by active transport, water follows via osmosis. Increased water pressure forces water into xylem and pushes it up to stem.
Transpiration pull- loss of water vapour at leaves replaced by water moving up xylem. Cohesion-tension theory.
Capillary action- adhesion of water to xylem vessels as they are narrow.
What is vacuolar pathway?
Vacuole to vacuole but has high resistance so rarely used.
What is the cambium?
It is the tissue layer that provides partially undifferentiated cells for plant growth. Found in the area between xylem and phloem. Forms parallel rows of cells which can differentiate into xylem or phloem for growth or repair.
What is the stele?
Area in the centre of root/stem tissue containing vascular portions.
