Topic 4.6-7 Transfer of materials between the circulatory system and cells, transport in plants Flashcards
What is a tissue fluid?
A watery substance containing glucose, amino acids, oxygen, and other nutrients. It supplies these to cells while also removing any waste materials.
What types of pressure influence formation of tissue fluid?
Hydrostatic pressure = higher at arterial end of capillery than venous end.
Oncotic preassure = changing water potential of the capillaries as water moves out.
How is tissue fluid formed?
As blood is pumped through increasingly small vessels, hydrostatic preasure is greater than oncotic preasure, so fluid moves out of capilliaries. It then exchanges substances with the cells.
What happens to excess tissue fluid?
It is removed through vessels into the lymphatic system, then returned to the blood near the heart.
Relate the structure of the xylem to their function
- Long, continuous columns made of dead tissue, allowing transportation of water
- Contains pits, allowing water to move sideways between vessels
- Thickened with a tough substance, providing structural support
Relate the structure of the phloem to their function
- Sieve tube elements transport sugars around the plant
- Companion cells designed for active transport of sugars into tubes
- Cytoplasm linked by plasmodesmata, allowing flow of substances between cells
Explain what is meant by the apoplastic pathway
A method of osmosis through the root hair cells, where water moves through the cell walls and intercellular spaces.
This pathway can only be used until water reaches the Casparian strip.
Explain what is meant by the symplastic pathway
A method of osmosis through the root hair cells, where water moves through the cytoplasm. To begin this pathway water must be actively transported into cells.
Explain the cohesion-tension therory
Water molecules form hydrogen bonds with each other, causing them to ‘stick’ together (cohesion). The surface tension of the water also creates this sticking effect. Therefore as water is lost through transpiration, more can be drawn up the stem from the roots.
How does root preasure affect water movement?
High mineral content gives the root a low water potential, meaning there is a strong osmotic flow into the roots. This creates a weak push effect, moving water from the roots to the stem.
How does temperature effect rate of transpiration?
A higher temperature increases, random motion and rate of evaporation, therefore increasing rate of transpiration.
How does light affect rate of transpiration?
A higher light intensity increases rate of photosynthesis, causing more stomata to open for gas exchange, therefore increasing rate of transpiration.
How does humidity affect rate of transpiration?
High humidity means that the water content of the air next to the leaf is high. This reduces the concentration gradient, therefore decreasing rate of transpiration.
How does air movement affect rate of transpiration?
Large amounts of air movement blow moist air away from the leaves, creating a steep concentration gradient. Therefore increases rate of transpiration.
Summarise the mass-flow hypothesis of translocation
- Sugar loaded into sieve tubes via active transport
- Lowers water potential, causing water to move in from xylem
- Hydrostatic preasures causes sugars to move
