Transport (General + Flowering plants) Flashcards
Why can unicellular organisms rely on diffusion for the movement of substances into and out of cells?
- They have a very high surface area to volume ratio, meaning diffusion, osmosis and active transport happen at a suffficient rate for the organism
- This means they do not need transport systems or specialist exchange surfaces to meet their needs
A high surface area to volume ratio means a small distance from the surface of the organism to the center of the organism
Why do multicellular organisms need transport systems and specialised exchange surfaces and what are examples of these?
- They have relatively low surface area to volume ratios meaning they cannot rely on diffusion, osmosis and active transport alone to meet their needs
- Because of this, they use transport systems to transport substances around the body, like the circulatory system and xylem/phloem
- They also need specialised exchange surfaces which do use diffusion, osmosis and active transport such as alveoli, villi and root hairs
What is the role of phloem?
Phloem transports sucrose and amino acids from the photosynthesising leaves to the non-photosynthesising parts of the plant (translocation)
- Phloem is made of living cells and is not hollow
- The phloem tubes are found on the outside of the stem
What is the role of xylem?
Xylem transports water and minerals from the roots to the leaves
- Xylem is dead and is hollow
- The xylem tubes are strengthened by lignin
What are root hair cells and how do they help plants absorb water?
- They are single celled extensions of cells in the root with a fingerlike projection
- They signifigantly increase ths surface area by which water and minerals in the soil are able to be absorbed by osmosis and active transport
What is the process of transpiration?
- Transpiration is the evaporation of water off the surface of a plant
- Water travels up the plant through xylem to the leaf and then evaporates off the surface of the spongy mesophyll, travels through the air spaces and then diffuses out the stomata (assuming a concentration gradient is present)
The water travels up the xylem due to the negative pressure created by transpiration (transpirational pull)
What is the purpose of transpiration?
- Replace water that is lost by previous transpiration
- Keeping cells turgid (inlcluding guard cells)
- Providing water for photosythesis (Less than 1%)
How does air movement/wind speed and intensity affect transpiration?
- The more wind, the higher the rate of transpiration
- This is because good airflow removes water vapour from the air surrounding the leaf (higher rate of evaporation) which increases the concentration gradient from the inside to the outside of the leaf, speeding up diffusion/osmosis
How does humidity affect transpiration?
- The higher the humidity, the lower the rate of transpiration
- This is because there will be more moisture outside the leaf, decreasing the concentration gradient from inside to outside the leaf (decreasing diffusion)
How does light intensity affect transpiration?
- The higher the light intensity, the higher the rate of transpiration
- This is because the stomata will open with high light intensities to allow CO₂ in, which allows more water to diffuse out
How does temperature affect transpiration?
- The higher the temperature, the higher the rate of transpiration
- This is because the particles have more kinetic energy so the water molecules move faster, evaporate faster and diffuse out of the leaf faster
Outline an experiment to measure the effect of wind intensity on the rate of transpiration
- Set up a potometer
- Cut a shoot underwater (to prevent air/water entering xylem)
- Ensure it is airtight
- Dry the leaves as wet leaves will skew results
- Measure the distance travelled by an air bubble up the tube in 1 minute
- Repeat the experiment
