b3

• Enzymes

  Biological catalysts that the rate of a chemical reaction go faster without being permanently altered themselves.
• What is the active site of an enzyme?

  Region of an enzyme which a substrate molecule binds and the reaction takes place.
• Why are enzymes described as having a high specificity for their substrate?

  Only substrates with a specific complimentary shape can fit into the enzymes active site.
• Describe lock and key model.

  1. Active site of the enzyme and the substrate come into contact.
  2. Substrate binds, enzyme substrate complex forms.
  3. Substrates converted to products.
  4. Products released from active site.
• Factors that affect enzyme controlled reaction

  • Temperature
  • pH
  • substrate concentration
• Explain how increasing temperature increases rate of enzyme controlled reaction

  • As temperature increases, molecules have more KE.
  • Movement of molecules increases
  • Probability of successful collision increases
  • More enzyme substrate complexes form
  • RoR increases
• Explain how increasing temperature above the rate of optimum increases rate of enzyme controlled reaction

  • Temperature increases above the optimum
  • Increased vibration breaks bonds
  • Active site changes shape, enzyme denatures
  • No more enzyme substrate complexes form
  • RoR decreases
• Explain how pH affects the rate of an enzyme controlled reaction.

  • Enzymes have an optimum pH.
  • pH shifts from optimum
  • Bonds are altered
  • active site changes shape, enzymes denatured
  • ror decreases
• Explain how substrate concentration affects the rate of an enzyme controlled reaction.

  • Substrate concentration increases
  • Number of substrate molecules in the volume increases
  • Probability of successful collision increases
  • More enzyme substrate complexes form
  • Rate of Reaction increases
  • Once all active sites are full, rate of reaction plateau.
• Describe the two main stages of photosynthsis?

  The first stage requires light and chlorophyll (located in chloroplasts in plant cells) to split water molecules into hydrogen and oxygen. The hydrogen is transferred to the second stage, but the oxygen is released into the atmosphere as a waste product. The second stage combines carbon dioxide with hydrogen to make glucose.
• Formula of photosynthesis ?

  6CO2 +6H20---> C6H12O6+ 6O2
• Equation for photosynthsisis?

  carbon dioxide + water------> glucose + oxygen
• Where does photosynthesis occur?

  Chloropasts
• Explain how water and mineral ions are taken up by plant?

  The way in which photosynthetic organisms take in nitrogen (to make proteins) illustrates the process of active transport. Producers get nitrogen from nitrate ions (NO3–). Molecules of water and gases can diffuse through partially-permeable cell membranes but nitrate ions cannot; producers use energy from molecules of ATP to transport nitrate ions through the cell membrane by active transport.
• What is the function of a xylem ?

  Xylem:

  • Made up of dead cells
  • contains lignin
  • transports water and minerals
  • Function is transpiration (loss of water)
  • One way flow
• What is the function in the phloem?

  • Made up of living cells
  • Does not contain lignin
  • has companion cells
  • Translocation occurs
  • Transports dissolved sugar/csrbohydrates
  • two way flow
  • End walls with pores
• State the limiting factors of photosynthesis?

  • Light
  • Temperature
  • co2 intensity
• Describe the relationship between increasing light intensity and the rate of photosynthesis?

  The rate of photosynthesis increases with increasing light intensity/ is directly proportional to light intensity up to a point at which the rate levels off
• Explain how the starch test can be used to show that plants need light to photosynthesise?

  • Plant produces glucose during photosynthesis. Some of this glucose is stored as starch.
  • If you use the starch test on a leaf grown without light, the leaf will not turn blue-black.
  • This means that there is no starch present in the leaf.
  • As no starch has been made in the leaf grown without light, it shows that light is needed for plants to photosynthesise.
• What is diffusion?

  Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
• What is osmosis?

  Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.
• What is active transport?

  Active transport is the movement of particles across a membrane against a concentration gradient. From an area of lower to an area of higher concentration using energy transferred during respiration.
• What is the function of the root hair cell?

  Root hair cells take up water and ions through their roots. The cells on plant roots grow into long hairs which stick out into the soil. This gives the plant a big surface area for absorbing water and mineral ions from the soil.
• Transpiration

  Loss of water from the plant.
• How is transpiration caused and transpiration stream?

  Evaporation and diffusion of water from a plant's surface. Most transpiration happens at leaves. This evaporation and diffusion creates a slight shortage of water in the leaf and so more water is drawn up from the rest of the plant through the xylem vessels to replace it. This in turn means more water is drawn up from the roots and so there's constant transpiration stream of water through the plant.
• Stomata

  1. Stomata around surrounded by guard cells which changes shapes to control size of the pore.
  2. When guard cells are turgid ( swollen with water) the stomata are open and when guard cells are flaccid stomata are closed.
  3. Stomata close automatically when supplies of water start to dry up - also sensitive to light and close at night to save water without losing out on photosynthesis.
• How do changes in the concentration of ions inside the guard cells help to open and close the stomata?

  • In response to stimuli like light, potassium ions (K+) are pumped into the guard cells.
  • This increases solute concentration of the guard cells, which decreases concentration of water molecules.
  • Water then moves into guard cells by osmosis. This makes guard cells turgid and stoma opens.
  • When potassium ions leaves the guard cells, the concentration of water molecules in the cell increases.
  • Water then moves out by osmosis,, guard cells become flaccid and stoma closes.
• Transpiration is affected by three main things?

  • An increase in light intensity
  • An increase in temperature
  • An increase in air movement
• Describe how temperature increases rate of transpiration.

  • Temperature increases
  • Water molecules have more kinetic energy so diffuse out of the stomata more quickly.
  • Photosynthesis also increases so more water is taken up from the soil pushing water up the xylem.
  • More water vapour diffuses out of the xylem
  • Rate of transpiration increases
• Describe how air movement increases rate of transpiration.

  • Air movement increases
  • High water concentration gradient maintained between the air spaces in the leaf and the atmosphere
  • Increased rate of diffusion of water molecules out of the stomata
  • Rate of transpiration increases
• Describe how high light intensity affects rate of transpiration

  • High light intensity means greater number of stomata are open to allow gas exchange for photosynthesis
  • As photosynthesis increases, more water is taken up from the soil, pushing water up the xylem.
  • More water vapour diffuses out of the stomata
  • Rate of transpiration increases
• Describe how low light intensity affects rate of transpiration

  • At a low light intensity, fewer stomata are open so the rate of transpiration decrease.
• What is translocation?


  The movement of food substances around a plant.
• Describe how a potmeter can be used to to investigate the rate of transpiration?

  Measure the distance the bubble moved over a given time.
• Individual - A single organism

  Population - All the organisms of one species in a habitat

  Community- All the organisms (different species) living in a habitat

  Ecosystem- A community of organisms along with all the non living conditions.
• How do abiotic factors affect community?

  1. Environmental conditions - Raise of temperature, light intensity, soil pH and moisture levels.
  2. Toxic chemicals - e.g. chemical pesticides or fertilisers. Pesticides can build up in food chains so organisms at the top also receive toxic dose. Excess fertilisers released into lakes and ponds caused increased growth of algae. This is called eutrophication. The algae block the sunlight from the plants which die. Microorganisms feeding on the dead plants use up the O2 leading death of other organisms.
• How do biotic factors affect community?

  1. Availability of food
  2. Number of predators
  3. Presence of pathogens
• What are organic molecules?

  Molecules that contain carbon. E.g carbohydrates, lipids and proteins.
• Long chain carbohydrates are made from simple sugars.

  Proteins are made from amino acids

  Lipids are made by joining fatty acids and glycerol.
• State all the Food tests?

  • Sugar- Benedict solution
  • Colour change: Blue to red
  • Starch- Iodine solution
  • Colour change: Orange to black
  • Protein- Biuret solution
  • Colour change: Blue to purple
  • Fats- Ethanol
  • Colour change: Milky emulsion