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Flashcards in Paper 2 Collection Deck (196)
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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
  • Having thinner leaves