B4

B4

1. Cells

   • All cells contain DNA and organelles
     • DNA molecules are on the form of a double helix and contain the genetic code
     • Organelles are the different parts of a cells structure
       • Work together to allow the cell to perform a specific function
   • Animal cells
     • Cytoplasm
       • Where most chemical reactions take place including anaerobic respiration
     • Mitochondria
       • Contain the enzymes needed for aerobic respiration
     • Nucleus
       • Contains the DNA that carries the genetic code for making enzymes and other proteins needed in all chemical reactions
     • Cell membrnae
       • Allows chemicals like gases and water to pass in and out freely
         • Prevents other chemicals leaving or entering the cell
   • Plant cells
     • Contains everything in an animal cell and more
     • Cell wall
       • Made of cellulose to strengthen the cell
     • Permanent vacuole
       • Helps support the cell
     • Chloroplasts
       • Contains the green pigment chlorophyll which absorbs light energy
       • Contains some enzymes needed for photosynthesis
   • Microbial cells
     • E.g. Bacteria
     • Cell wall - not made of cellulose but other material e.g. Protein
     • DNA - in a circular structure, not in a nucleus and not as chromosomes
     • Yeast cells are more similar to higher organisms but are still classed as microbial cells

2. Enzymes

   • Protein molecules that speed up the rate of chemical reactions in cells
   • Cells produce enzymes according to the instructions carried in genes
   • Need a specific temperature to work at their optimum
     • Different enzymes have different optimum working temperature
     • At low temperatures, small increases in temperature cause an increase in the frequency and energy of collisions
     • After the optimum temperature is reached, enzymes start to become damaged so the reaction starts to slow down
       • Eventually the enzymes structure is permanently destroyed and it becomes denatured - stops workong
   • The lock and key model
     • Only a molecule with the correct shape can fit into an enzyme
     • Once te enzyme and molecule are linked...
       • A reaction takes place
       • The products are released
       • The process is able to start again
       • The enzyme is reused
     • The active site
       • The place where the molecule fits into the enzyme
       • Each enzyme has a different shape so it's highly specifuc
       • The shape of the active site can be changed irreversibly by...
         • Heating the enzyme above a certain temperature
         • Altering the pH level
         • This means the molecules can no longer fit and a reaction can't take pkace

3. Respiration

   • The release of energy from food chemicals in all living cells
   • Aerobic respiration
     • Releases energy inside living cells by breaking down glucose and combing the products with ixygen
     • Glucose + oxygen = carbon dioxide + water + energy released
     • Needs oxygen
     • Occurs in animal cells, plant cells and many microbial cells
     • Energy released is used in....
       • Movement - the contraction of muscles when running
       • The synthesis (making) of large molecules from smaller ones
       • Active transport of some chemical molecules across a cell membeane
   • Anaerobic respiration
     • Releases energy inside the cytoplasm of living cells by breaking down glucose molecules WITHOUT oxygen
     • Plant cells and some microbial cells e.g. Yeast
       • Glucose = carbon dioxide + ethanol + energy released
     • In animal cells and in some bacteria
       • Glucose = lactic acid + energy released
     • Occurs in conditions of very low oxygen or where no oxygen is present
       • When plant roots are in water logged soil e.g. Rice plants
       • In human muscle cells during vigorous exercise e.g. 100m sprint
       • In bacterial cells inside a puncture wound
     • Uses
       • Provides a little more energy to cells when necessary e.g. To limb muscles when running away form danger
       • Yeast in bread dough releases carbon dioxide gas which makes the dough rise before baking
       • Anaerobic microbes added to solid matter in sewage farms
         • Microbes break down the sewage and release methane gas which is collected and called biogas
           • Burned to heat water to turn a generator for electricity
           • Used as a fuel to replace petrol in vehicles
       • Anaerobic respiration in yeasts is also used to produce alcohol
         • Known as fermentation
         • If oxygen gets in, the yeast stops respiring anaerobically and the alcohol turns to vinegar
   • AEROBIC RESPIRATION is much more efficient and releases much more energy per glucose molecule than ANAEROBIC RESPIRATION

4. Synthesis of large mileculs

   • Glucose can be built up into a polymer as cellulose (building plant walls) of starch (storage in roots)
   • Glucose and nitrates can be joined to make larger molecules of amino acids
     • Amino acids can be joined together to make proteins in plant, animal and bacterial cells
   • Glucose = starch

5. Photosynthesis

   • Light energy is absorbed by chlorophyll in green plabss
     • Within the chlorophyll molecule, the light energy is used to rearrange the atoms of carbon dioxide and water to produce glucose
       • Oxygen is produced as a waste product
   • Carbon dioxide + water ==light energy== glucose + oxygen
   • Limiting factors
     • Temperature
       • As the temperature approaches 45°C the enzymes controlling photosynthesis are denatured
         • The rate of photosynthesis drops
     • Carbon duoxide
       • A rise in carbon dioxide levels has no effect after a certain point so is no longer a limiting factor
       • As the carbon dioxide concentration rises, so does the rate of photosynthesis
     • Light intensity
       • A rise in light intensity has no effect after a certain point so is no longer a limiting factor

6. Diffusuon

   • Overall movement of substances from regions of HIGH CONCENTRATION TO LOW CONCENTRATION
   • Oxygen and carbon dioxide are exchanged in the leaf by diffusion of the gases in and out
   • Substances that move in and out of cells include oxygen, carbon dioxide and dissolved food
   • Energy use in plants
     • Plants need to absorb nitrates from the soil for healthy frowth
     • Normally absorb nitrates through diffusion
     • However the concentration of nitrates outside the plant is lower that that jnside
       • A plant has to use energy from respiration to absorb nitrates through ACTIVE TRANSPORT
   • Active transport
     • Movement of a substance from a region of LOW CONCENTRATION TO HIGH CONCENTRATION
       • Needs energy from respiration to do this
     • If concentration of glucose inside a cell is higher than the concentration outside, the glucose would diffuse out of the cell because of diffusion
       • Cells use active transport to bring all the glucose back inside the cell

7. Collecting data on how light effects plants

   • Light levels can be measured using a LIGHT METER
   • Plants can be identified using an IDENTIFICATION KEY
   • Plants are chosen at random by using a QUADRAT and TRANSECT
     • A quadrat is anything within a defined area (e.g. A meter square) which is placed at intervals along a transect line tandomlu
     • A transect if a random section across an area (e.g. A line or measured band) which is used to represent the entire album
   • These techniques are used to ensure that the data produced is representative of the area
     • But is also random to avoid any bias in the findings

8. Osmosis

   • Type of diffusin
   • Overall movement of water from a DILUTE SOLUTION TO A MORE CONCENTRATED SOLUTION through a partially permeable membrane
   • The membrane allows the passage of water molecules but not solute molecules which are too latge
   • The water moving due to osmosis gradually dilutes the concentrated solution