B6: Plant Structures And Their Functions Flashcards
What is photosynthesis?
A chemical reaction that tasked place inside a plant converting light energy into chemical energy
Why is photosynthesis important?
Produces glucose which is used in respiration to release energy.
Converted to starch and stored.
Where does photosynthesis take place ?
Chloroplast
What type of reaction is photosynthesis?
Endothermic reactions
What is chlorophyll?
A pigment found in chloroplasts that absorb light
What factors affect the rate of photosynthesis?
1.temperature
2.light intensity
3.carbon dioxide concentrations
What is a limiting factor ?
A variable that limits the rate of a reaction
How does temperature affect the rate of photosynthesis?
> Higher temperatures can cause enzymes to be denatured and rate of photosynthesis decreases
How does light intensity affect the rate of photosynthesis?
Rate of photosynthesis is directly proportional to light intensity
How can the effect of light intensity on the rate of photosynthesis be measured in the lab ?
> using a light meter
using the inverse square law where:
Light intensity is directly proportional to 1over distance squared
Why does the rate of photosynthesis decrease as the distance from a light source increases?
Light intensity is inversely proportional to the square of the distance from the light source
How does carbon dioxide concentration affect the rate of photosynthesis?
As carbon dioxide concentration increases the rate of photosynthesis increases
Why do plants require water ?
Photosynthesis, maintenance of structure
Why do plants require minerals ions ?
For growth
Which structure in plants is adapted for the uptake of water and minerals?
Root hairs
How is water transported into root hairs ?
Osmosis
How are minerals transported into the root hair ?
Active transport
How are roots adapted for the absorption of water and minerals?
Long hairs that extend from the cell body to increase surface area and absorption
What are the 2 transport tissues?
Xylem and the Phloem
What is the function of the xylem?
Transport water and minerals up the plant from the root to the leaves via the transpiration stream
Describe how the xylem is adapted to its function ?
- Composed of dead cells laid end to end to form a hollow column
- Thick cell wall strengthened with lignin to provide support
What is the function of the phloem ?
Transported sugars up and down the stem from photosynthetic tissues via translocation
What are the 2 cell types that make up the phloem ?
Seine tube Elements and companion cells
How is the phloem adaptation of sieve tube elements good for its function ?
They are long thin tubes with perforated end plates to enable the flow of sugars
How is the phloem adaptation of companion cells good for its function ?
Contain a dense cytoplasm, nucleus and mitochondria.
They provide energy for processes in both cell types
What is transpiration?
The loss of water vapour from the parts of a plant exposed to the air due to evaporation and diffusion
Where does the most transpirtation take pace ?
Leaves
What is the process of transpiration?
- Water evaporates from the mesophyll cell surfaces and diffuses out of the stomata
- Water molecules are drawn up the xylem vessels to replace the water that has been lost
- This causes more water molecules to be absorbed from the soil into the root hair cells
What are stomata ?
They are pores found in the lower epidermis of a leaf which allow gas exchange
What are guard cells ?
Specialised cells surrounding the stoma that change shape to control the size of the pore
How do guard cells open the stomata ?
Water enters the cell and it then swells and becomes turgid meaning the cell bands and draw away from each other opening the stomata
How do guard cells open the stomata ?
Water enters the cell and it then swells and becomes turgid meaning the cell bands and draw away from each other opening the stomata
How do the guard cells close the stomata?
Water leaves the cell they become flaccid which closes the stomata
What factors affect the rate of transpiration?
Light intensity, temperature and air movement
What apparatus is used to measure the rate of transpiration?
Photometer
What equation is used to calculate the rate is transpiration using a Photometer?
Distance moved by bubble /time take
What are plant Tropisms ?
The growth of a plant in response to a stimulus
What is positive tropism?
The growth of a plant towards a stimulus
What is negative tropism?
The growth of a plant away from a stimulus
What are the 2 main types of plant tropism?
Phototropism and gravitropism
Define phototropism?
A plants growth response to light
Define gravitropism?
A plants growth response to gravity
What are auxins ?
A group of plants hormones involved inplants tropism
Control growth in plant roots and shoot tips
What are gibberellins ?
Plant hormones that control germination and flowering
Compare the effect of auxins in plant shoots and roots ?
Auxins stimulate growth in plant shoots and inhibit growth in plant roots
Where are auxins produced ?
Roots and shoot tips
How do auxins move through a plant ?
They diffuse through the plant in solution
Are plant shoots positively or negatively phototropic?
How does this affect shoot growth?
• Positively phototropic
• Plant shoots grow towards the light
Explain why plant shoots are positively phototropic?
• Shoot tip exposed to light
• On the shaded side of the shoot, auxin accumulates
• Elongation of cells on the shaded side
• Shoot tip bends towards the light
Are plant shoots positively or negatively gravitropic?
How does this affect shoot growth?
• Negatively gravitropic
• Plant shoots grow upwards, away from gravity
Explain why plant shoots are negatively gravitropic?
• Shoot placed horizontally
• Due to gravity, auxin accumulates on the lower side of the shoot
• Elongation of cells on the lower side
• Shoot bends upwards growing away from gravity
Are plant roots positively or negatively phototropic?
How does this affect root growth?
• Negatively phototropic
• Plant roots grow away from the light
Explain why plant roots are negatively phototropic?
• Root exposed to light
• On the shaded side of the root, auxin accumulates
• Inhibition of cell growth on the shaded side
• Root grows away from the light
Are plant roots positively or negatively gravitropic?
How does this affect root growth?
• Positively gravitropic
• Plant roots grow downwards, towards gravity
Explain why plant roots are positively gravitropic?
• Root placed horizontally
• Due to gravity, auxin accumulates on the lower side of the root
• Inhibition of cell growth on the lower side
• Root bends downwards growing towards gravity
Explain how plant tropisms increase the chance of survival?
• They enable plants to respond to their environment
• Shoot growth towards the light maximises light absorption
• Root growth downwards increases the uptake of water and minerals from the soil and enables anchorage of the plant body to the ground
Describe the role of auxins in commercial plant cultivation?
Rooting powders contain auxins that stimulates the growth of roots in cuttings
Used in selective weed killers that target and alter growth patterns
Describe the role of gibberellins in commercial plant cultivation ?
• Initiate germination in seeds at times of the year when they naturally wouldn’t. Ensure all seeds in a batch germinate.
• Trigger flowering in plants under irregular conditions. Also increase fruit size by reducing the number of flowers produced by plants.
• Produce seedless fruits by stimulating the growth of fruit from unpollinated flowers.
How do gibberellins trigger germination ?
In the presence of water, gibberellins break seed dormancy initiating germination
Why is ethene important in commercial plant cultivation?
• Ethene stimulates enzymes that control fruit ripening
• Enables fruits to be picked while they are unripe and less easily damaged. They can be stimulated to ripen during transportation to shops.
What is translocation?
The movement of sugars up and down a plant via the phloem (requires ATP)
Describe how leaves are adapted for photosynthesis and gas exchange?
• Broad - large SA for light absorption
• Thin - short diffusion distance for gases, allows light to reach all cells
• Vascular bundles (xylem and phloem) form a network to deliver water and remove glucose. Also provide support.
• Photosynthetic pigments (e.g. chlorophyll) absorb light
Describe how tissues of the leaves are adapted for photosynthesis and gas exchange?
• Palisade mesophyll layer - receives most light so contains greatest concentration of chloroplasts
• Upper epidermis - transparent, allows light to reach palisade layer
• Spongy mesophyll layer - air spaces increase the rate of diffusion
• Lower epidermis - contains many stomata for gas exchange
Describe how plants are adapted to live in hot, dry conditions?
• Small leaves/spines - reduce water loss
• Thick waxy cuticle - reduces evaporation,
• Shallow but widespread roots - large Surface area to absorb water
• Stomata close to reduce water loss
