Transport, food storage and gas exchange in flowering plants. Flashcards
Why do plants need to transport water CO2 O2 and certain minerals?
For metabolism, cell division, growth and reproduction
Why do roots have root hairs?
to increase the surface area for absorption
How are roots adapted to their function?
- They have no cuticle which would prevent the entry of water.
- They have thin walls
- The cytoplasm is more concentrated than the soil water
How is water absorbed into the roots
By osmosis
Describe root pressure
generated by water entering the root cells by osmosis which pushes the water up the xylem.
Define
What is transpiration
The looss of water from the leaves of a plant
Describe the process of transpiration
When water evaporates from the cells in a leaf, the cells become less turgid. They have a low water concentration creating an osmotic gradient.Water passes from the xylem into these cells by osmosis.
This pulling force is transmitted to water molecules all the way down through the stem to the roots.
(sucking water from a straw).
How is transpiration controlled?
By the opening and closing of stomata and a waxy cuticle. The stomata are open during the day and closed by night. In hot conditions the stomata will close during the day to prevent water loss.
Transport of minerals
Nitrates, phosphates, calcium, and magnesium ions are dissolved in water and transported from roots to other parts of the plant.
transport of CO2
Two sources of CO2 for photosynthesis
1. CO2 is obtained directly from respiring cells
2. CO2 can enter the leaf through the stomata from the air
Sources of CO2 in the atmosphere
- respiration by living things
- Burning of fossil fuels
Transport of photosynthetic products
- O2 dffuses out through the stomata or is used by cells for respiration
- Glucose is used for repsiration or converted to starch and stored. Glucose can be moved by diffusion in the phloem sieve cells.
Modified plant food storage organs
These organs store food from one growing season to the next to fulfill their life cycle [perennation]
Examples
* root- tap root- carrot
* stem- underground stem or tuber- potato
* leaf- bulb- onion
TACT
The cohesion tension model
Two Irsh scientists- henry Dixon and John Joly
1. When water evaporates through the stomata it results in more water being drawn across from the xylem
2. This “Transpiration Pull” puts the water in the xylem under a tension that is transmitted downwards to the roots. This causes a column of water to move up through the plant
3. Cohesion between water molecules prevents the column of water from breaking giving a continuous stream of water
4. The water column is also held up in the xylem vessels by the adhesion of water molecules to the surface of vessel walls.
Define cohesion and adhesion
Cohesion= The force of attraction between water molecules.
Adhesion=The force of attraction between water molecules and the molecules of another substance.
