Plant Systems 🌿 Flashcards
(24 cards)
Describe basic structure of a leaf by referencing its tissues.
- Epidermal tissue: covers whole plant.
- Upper - fewer stomata, waxy cuticle.
- Lower - lots of stomata for gas exchange.
- Paslisade mesophyll: lots of palisade cells, photosynthesis happens here.
- Spongy mesophyll: big air spaces for diffusion.
Additional:** vascular bundle** (xylem and phloem for transport, and meristem tissue, allows plant growth by differentiating).
Structures relating to functions:
Epidermal tissues
- UPPER: covered with waxy cuticle to prevent water loss, transparent to allow light in for photosynthesis in palisade mesophyll layer.
- LOWER: Many stomata for gas exchange (by diffusion).
eg. In dry conditions, plants have thicker waxy cuticles to prevent water loss.
Structures relating to functions:
Palisade mesophyll tissue
- Lots of chloroplasts for photosynthesis.
- Near the top of the leaf for best access to light.
Structures relating to functions:
Xylem and phloem
- Xylem is made of hollow tubes strengthened by lignin - this is where transport of water and minerals takes place.
- Phloem transports dissolved sugars from the leaves to other parts of the plant, small pores in end walls allow cell sap to flow through.
- Together, they form vascular bundles for the efficient transport of nutrients in a plant.
How are leaf tissues adapted for efficient gas exchange?
What do phloem tubes transport and what is the name of this process?
They transport cell sap (made up of water, sugars and amino acids) in a process called translocation where the substance is transported all around the plant in multiple directions.
What substances are transported in the transpiration stream?
Water and mineral ions.
Describe the the process of transpiration in simple steps.
- Water from a leaf evaporates and diffuses (mainly) through the stomata.
- This creates a slight shortage of water so more is drawn up through xylem tubes to replace it.
- This in turn means more water is drawn up through the roots (by osmosis), which maintains a constant transpiration stream through the plant.
How is transpiration just a side effect of photosynthesis?
Leaves have stomata in them for efficient gas exchange, and when they open water escapes from the plant as there is more water outside the plant than in.
What are the 4 main factors that affect the rate of transpiration?
- Light intensity
- Temperature
- Air flow
- Humidity
How does light intensity affect the rate of transpiration?
Brighter light = faster transpiration. Stomata open during photosynthesis, which can’t happen in the dark so they don’t need to be open to let CO2 in. When the stomata are closed very little water can escape.
How does temperature affect the rate of transpiration?
Higher temperature = faster transpiration. When it is warmer, particles have more kinetic energy to evaporate and diffuse out of the stomata.
How does air flow affect the rate of transpiration?
Better air flow = faster transpiration. When there is good air flow, the air which has lots of water waper in is constantly replaced which maintains a high concentration gradient between the plant and the air.
How does humidity affect the rate of transpiration?
Higher humidity = slower transpiration. When it is very humid there is lots of waper vapour outside of the plant (as well as inside), so diffusion happens slower as there is a lower concentration gradient.
How are guard cells adapted for gas exchange and controlling water loss in a leaf?
- When a plant is short of water guard cells become flaccid and cannot open, preventing water loss.
- When a plant has lots of water, they are turgid which allows water to diffuse out.
- They are light-sensitive so close at night when they cannot photosynthesize.
- Thick inner walls and thin outer walls make the opening and closing work.
What is photosyntheis?
The process that uses carbon dioxide, water and light energy to make glucose in a plant.
Is photosynthesis endo-thermic or exo-thermic.
Endo-thermic because it absorbs light energy (taking energy from the surroundings).
What are the word and symbol equations for photosynthesis?
6CO2 + 6H2O → C6H12O6 + 6O2 + 6H2O
What are the 3 main ways glucose is used in a plant?
- Respiration: Energy is released from the break-down of glucose.
- Making celluose: Glucose can be converted into celluose cell walls for plant growth.
- Making amino acids: Glucose is combined with nitrate ions to make amino acids, which in turn can make proteins.
How is glucose stored in a plant?
As lipids in the seeds (eg. sunflower oil in sunflower seeds), or as starch. Starch is better as it is insoluable so does not draw in water.
What are some limiting factors on the rate of photosynthesis?
If any of the following get too low or too high, they stop photosynthesis from happening so become a limiting factor:
- Light intensity
- Temperature
- Concentration of CO2
How does light intensity increase the rate of photosynthesis?
More light means more energy for photosynthesis (up to a certain point when other factors impact the rate of photosynthesis).
How do CO2 levels increase the rate of photosynthesis?
CO2 is needed in photosynthesis, so more means a faster rate (up to a certain point when other factors limit the rate of photosynthesis).
How does temperature affect the rate of photosynthesis?
Increasing the temperature increases the speed at which enzymes work. However, if it gets too hot, the enzymes get denatured and photosynthesis can no longer occur.
