SB6 - Plant Structures and their Functions ✓ Flashcards
SB6a - What is the equation for photosynthesis?
Carbon dioxide + Water → Glucose + Oxygen
SB6a - What is the equation for respiration?
Glucose + Oxygen → Carbon dioxide + Water
SB6a - What does photosynthesis do?
It traps energy from the sunlight and converts it to glucose
SB6a - Where does photosynthesis occur?
In the chloroplasts of the plant cell
SB6a - What type of reaction is photosynthesis?
- Endothermic.
- The products have more energy than the reactants.
- This means they have taken in energy from the surroundings during the reactions
SB6a - Why is glucose necessary?
- Glucose molecules are joined together to form a polymer of starch.
- After photosynthesis stops, this is broken down to simple molecules which are used to form sucrose.
- Sucrose is used to make:
- Starch (In a storage organ such as a potato)
- other molecules for the plant (cellulose, lipids etc.)
- Glucose for respiration (to release energy)
SB6a - How are leaves adapted for their purpose?
- They have a broad flat shape giving them a large surface area for photosynthesis
- There are lots of palisade cells near the top which are packed with chloroplasts to absorb light
- Stomata allow carbon dioxide to diffuse in for photosynthesis
- When there is light (during day) water flows into guard cells making them rigid and when there is less light (nighttime) The water flows out making it loose its rigidity
- When it is rigid, it is open so it is only open when there is light
- This means it will only allow carbon dioxide to diffuse when there is also light to conduct photosynthesis
- Leaves are thin meaning carbon dioxide doesn’t have far to diffuse
SB6a - Tomayto, tomahto?
Stomayto, stomatoh
SB6a - Why are the stomata an example of a gas exchange system?
They let carbon dioxide diffuse in and let oxygen diffuse out
SB6b - What are the three main limiting factors that affect photosynthesis?
- Carbon dioxide concentration
- Light Intensity
- Temperature temperature
SB6b - Why are plants less likely to grow higher up on a mountain?
Higher up, the air pressure is lower meaning the carbon dioxide concentration is lower
SB6b - A graph showing how increasing rate of light intensity affects rate of photosynthesis eventually levels out. Why can’t it get any higher despite light intensity increasing?
- As the graph curves, light intensity is the limiting factor.
- Once it levels out, something else is the limiting factor.
SB6b - Once the rate of photosynthesis can’t increase anymore (due to light intensity in this case) how would you increase the rate of photosynthesis?
- Something else is the limiting factor.
- Increasing the CO2 concentration or increasing the temperature will allow the rate of photosynthesis to continue to increase.
- Eventually it will level out again as something else has become the limiting factor.
SB6b - Why is it that even if temperature is the limiting factor, you’ll get to a point where increasing it won’t increase the rate of photosynthesis?
- At a temperature that is too high, the enzymes in the plant become denatured.
- They can no longer bind to their substrate and therefore processes can’t occur anymore
SB6b - What is the inverse square law, and where does it apply to?
- The inverse square law is used to find out how light intensity chages ith distance from the source.
- I: light intensity
- d: distance
I(original) x d(original)² = I(new) x d(new)²
- light intensity is inversely proportionate to the square of the distance
SB6b CP - Describe a method, using algae balls and hydrogen carbonate indicator, to investigate rates of photosynthesis at differing light intensities.
- Add 20 algae balls and the same amount of indicator to as many glass bottles as you need
- Compare the colour of the bottle at the start to a key to work out its starting pH (they should all be the same)
- Place a tank of water between the light and the first glass to absorb the heat given off by the light
- Cover one with foil so it is in the dark and place it next to the one closest to the lamp
- Measure out the distances you place all of the bottles
- Turn on the light and wait till you see noticable changes in the pH
- Once you’ve decided to stop, work out the pH again by comparing to a key
- Work out the change in pH/hour to be your rate of reaction
- Plot a graph of rate of reaction vs distance from light
SB6c - Why do plants need to take in water?
To be used in/to:
- Carrying dissolved mineral ions
- Keeping cells rigid so plants don’t wilt (droop)
- Cooling leaves (when it evapourates)
- Photosynthesis
SB6c - How are roots adapted to absorb water?
- Roots have root hair cells
- The hairs make the surface area larger meaning there is more area for mineral ions to be quickly absorbed through water
SB6c - What is a concentration gradient and what can it cause to occur?
When two areas are connected in some way and having differing levels of concentration of a substance, they have a concentration gradient If this is in a fluid, diffusion can occur, where the substance moves from the area of higher to lower concentration
SB6c - What do root hair cells and root cells have between them and why?
They have a little tube allowing diffusion of fluids between cells
SB6c - How can some water enter the root hair cells if not through openings?
The root hair cells have a semi-permeable membrane meaning that osmosis can take place with the water moving down the concentration gradient into the cytoplasm of the cell
SB6c - How do plants take in mineral ions?
- Through the water they absorb.
- However as there is a higher concentration of these in the plant than in the soil, they can’t absorb it through diffusion but rather through active transport which takes up energy
SB6d - Describe the process of transpiration
- The flow of water into a root, up the stem and out the leaves
- As water on the leaves’ surface evapourates, a concentration gradient is created
- This prompts water to be drawn out from the inside of the leaves through the stomata through diffusion and osmosis
- They travel through the xylem down the concentration gradient
- This is aided by the cohesion between the H2O molecules due to hydrogen bonds and adhesion to the walls of the xylem cell
- At the root hair cells, as water moves up the xylem, water is also taken in due to the concentration gradient
SB6d - Describe the process of translocation
- The transport of sucrose around a plant
- The source is the leaf where glucose is created by photosynthesis
- Glucose monomers join together to from a sucrose polymer (as only polymers can be transported this way)
- The sucrose is actively transported into the phloem through a companion cell
- At the top of the phloem there is a low concentration of water. So water from the xylem diffuses through pores in the cells
- This water then has a high pressure so moves down the phloem taking the sucrose with it
- It will then be actively transported through a companion cell to whatever cell it is needed in
SB6d - Describe the adaptations of the xylem
- Multiple pores to allow water and mineral ions to enter and leave
- dead cells, no cytoplasm and no cell walls to allow flow of water through it
- rings made of lignin and thick side walls to keep the water inside
SB6d - Describe the adaptations of the phloem
- Holes in cell walls to allow liquids to flow
- No nucleus or cytoplasm as they aren’t needed and would be a waste of energy
- Companion cells to pump have many mitochondria so they have energy to actively transport sucrose
SB6d - Describe how you can investigate rates of transpiration
- A potometer is used for this. It involves using a plant attached to a rubber stopper connected to a reservoir of water and a capillary tube.
- The capillary tube should have at least one bubble in it and should have a scale .
- As the plant uses up water it will draw water from the tube moving the air bubble.
- The speed of the bubble will allow you to calculate the rate of transpiration
SB6e - How is the structure of a leaf adapted for photosynthesis and gas exchange?
- Leaves are broad and flat which gives them a large surface area.
- Palisade cells near the top of the leaf are packed with chloroplasts to allow large amounts of light absorption.
- Spongy cells create air spaces so gasses can diffuse in and out.
SB6e - Why do some plant have needle shaped leaves?
- Small leaves result in a reduced surface area so transpiration happens more slowly.
- A thick cuticle protects them from infection.
- The smaller leaves helps them to withstand strong winds and a lack of water
SB6e - How do plants reduce water loss?
- Having stomata located inside small pits
- By losing leaves in winter
- By closing stomata at night
SB6f - What are the names of three main plant hormones?
- Auxins: promote growth
- Gibberellins: cause germination
- Ethene: cause fruit ripening
SB6f - What are positive and negative phototropism and gravitropism?
- Positive = towards
- Negative = away
- Phototropism = a response to light
- Gravitropism = a response to gravity
SB6f - How does phototropism occur?
- Auxins a produced in the tip of the shoot
- As the shoot is exposed to light, auxins move to the shaded side of the root (the side away from the sun)
- Here they cause the cells to elongate causing the shoot to point towards the sun
SB6g - How are auxins used by plant growers?
- Selective weedkillers contain artificial auxins to kill plants with broad leaves.
- Auxins are also used in rooting powders which cause plant cuttings to grow roots rather quickly
SB6g - What are the uses of gibberellins?
- Produce seedless fruits
- Promote flowering
- Increase fruit size
- Germinate seeds
SB6g - How do farmers ripen fruits once they have been removed from a tree?
Use ethene gas
SB6d - Describe the factors that affect transpiration.
- Light intensity: stomata opens wider allowing water in quicker
- Temperature: More evapouration means a greater concentration gradient on the leaf surface
- Wind speed: Less water on leaf surface steepens the concentration gradient
- Fall in humidity: As the air becomes less saturated, water vapour evapourates more easily steepening the concentration gradient
SB6f - How does gravitropism occur?
- Auxins in the root are pulled down by gravity.
- They inhibit cell elongation here causing the root to grow downwards
- Auxins in the shoot are also pulled down by gravity but here they cause cell elongation making the shoot grow upwards
SB6f - Describe Darwin’s experiments with auxin and what can be concluded from the results.
- Three intact shoots exposed to light. One covered with a black cap, one with a transparent cap and one normal
- The one with the black cap didn’t bend towards the light while the other two did
- This shows that auxins are dependent on light to work
- One where the tip was removed didn’t bend towards the light.
- This showed that auxins are produced in the tip of the shoot
- A tip was also placed on a permeable and and impermeable base (removed from the plant)
- The one on the permeable base (agar block) bent towards the light but the other didn’t
- This shows that auxins need to travel further down in the plant to work
