Biology Paper 1

• Eukaryotic cells are found in plants, animals, fungi and protists

  Prokaryotic cells are bacterial, they have plasmids, do not contain mitochondria (respiration), chloroplast (photosynthesis) or a nucleus
• Bacterial cells:

  Cytoplasm - chemical reactions take place

  Flagella - movement

  Plasmids - DNA

  
  

  Animal cells:

  Cell membrane - controls what comes in and out with receptor molecules

  Ribosomes - synthesising proteins

  Mitochondria - aerobic respiration

  
  

  Plant cells:

  Permanent vacuole - fluid filled sac that holds water
• Magnification - how many times larger an object is through a microscope

  Resolution - ability to distinguish between 2 or more objects

  Light microscope - magnifications of up to 400x

  Electron microscope - magnifications of up to 500000x - allow scientists to see structures like mitochondria, chloroplasts and ribosomes
• Active site is the part of the enzyme that binds to the substrate


  Factors affecting the rate of enzyme action:

  Temperature -optimum of 37 degrees

  pH - e.g. pepsin breaks down proteins in the stomach, and works best in stomach acid as its optimal is a pH of 2
• Investigating the effect of pH on amylase:

  add amylase to the starch solution every 30 seconds

  take a drop of the mixture and add a drop of iodine

  record the time taken for the iodine to stop turning blue (indicating that all the starch has broken down)

  to find amylase's optimal pH, repeat using different pH's; the shorter time taken for the iodine to stop changing colour, the faster the amylase has broken down the starch
• Digestive enzymes are produced by specialised cells (perform a specific function) in the glands and the lining of the gut.

  • The digestive enzymes catalyse (speed up) the breakdown of large, insoluble food molecules (polymers) into smaller, soluble molecules (monomers) that are then small enough to be absorbed into the bloodstream.
  • Digested molecules can be used to construct new carbohydrates, proteins and lipids in the body.
  • Some glucose produced by digestion is used for respiration.
• • Amylase turns starch into maltose.
  • It's released by the salivary glands (in the mouth) and the small intestine.
  • Protease turns protein into amino acids.
  • It's released in the small intestine, pancreas and stomach.
  • Lipase turns lipids into glycerol and fatty acids.
  • It's produced in the small intestine and pancreas and stomach
• Bile is an alkaline substance produced in the liver and stored in the gall bladder. Bile is important because:


  Optimal enzyme conditions:

  • Enzymes in the small intestine operate best in alkaline conditions.
  • Bile neutralises acid from the stomach to stop these enzymes becoming denatured (lose their activity).

  Emulsification:

  • Bile breaks up fats into tiny droplets, through a process called emulsification.
  • The tiny droplets have a higher surface area than the original fat drop.
  • This increases the rate of the lipase-catalysed reactions that break fats down.
• • To test for starch, add iodine solution.
  • It will turn blue-black if starch is present.

  • To test for lipids, add Sudan III.
  • If lipids are present, a red-stained oil layer will float on the water surface.
  • To test for proteins, add Biuret solution.
  • It will turn mauve or purple if proteins are present.
  • To test for sugar, add Benedict’s reagent and heat for about two minutes.
  • It will turn any of green, yellow or red if sugar is present.
  • The colour depends on the concentration.
• Many factors can affect the rate of enzyme activity, so when investigating the rate of enzyme activity several factors need to be kept constant
• pH

  • Every enzyme has an optimum pH
  • Extremes of pH will cause the enzyme to denature
  • pH can be kept constant by using a buffer
• Temperature

  • Increasing the temperature will initially increase the rate of enzyme activity as the enzymes will have more kinetic energy
  • Above a certain temperature, enzymes denature as the high temperature breaks the bonds holding together the enzyme
• Enzyme concentration

  • Increasing the enzyme concentration increases the number of active sites available, which causes the rate of reaction to increase
• Substrate concentration

  • Increasing the substrate concentration increases the rate of enzyme activity, as there are more substrate molecules to bind to the enzyme active site
• If an investigation wishes to examine the effect of one of these factors on enzyme activity, all others must be kept constant
• As the substrate concentration increases, the rate of enzyme activity will initially increase.

  However, the rate of enzyme activity will eventually plateau. This is because at a certain substrate concentration all of the active sites will be occupied with substrate molecules. We would say that the enzymes are saturated.

  So even if a higher concentration of substrate molecules was added, the extra substrate molecules would not be able to bind to any enzymes as all the active sites would be full.
• • Phagocytes are immune cells that ingest and kill invading pathogens (disease-causing microorganisms).
• 
  

  Cells and organisms need energy for many reasons:

  Construction

  To make larger molecules from smaller molecules. For example:

  • Glucose molecules can be joined together to produce starch (in plants).
  • Proteins can be made from amino acids in plants and animals

  Contraction

  Homeostasis

  Respiration
• Respiration is an exothermic reaction

  Aerobic respiration - Glucose + Oxygen = Carbon Dioxide and Water (+energy)

  Anaerobic respiration in plants - Ethanol + Carbon Dioxide= Glucose (in yeast this is called fermentation)

  Anaerobic respiration in animals - Glucose is converted into lactic acid - Glucose is not broken down completely, making it a less efficient way of transferring energy than aerobic respiration.
• Aerobic respiration fully breaks down glucose whereas Anaerobic respiration partially breaks down glucose.

  Aerobic respiration produces much more adenosine triphosphate (ATP, which is a unit of energy) than anaerobic respiration.
• The main responses to increase the rate of respiration are:

  Increased heart rate

  Increase in breath volume

  Increase in breathing rate

  Blood vessels dilate
• • Lactic acid is toxic and can build up in muscles, leading to muscular pain and fatigue.
  • Lactic acid also stops muscles contracting efficiently.
  • Oxygen debt refers to the extra oxygen required after exercise to oxidise (combine with oxygen) lactic acid and remove it from cells.
  • Blood transports the lactic acid to the liver, where it reacts with oxygen to produce carbon dioxide and water.
  • Heavy breathing after exercise helps to repay the oxygen debt by taking more oxygen into the lungs.
• Metabolism is the sum of all the chemical reactions that happen in an organism. Many of these chemical reactions create new molecules with the help of enzymes. Metabolic reactions include:

  • Combining glycerol and fatty acid chains to make lipid molecules.
  • Combining glucose and nitrate ions to make amino acids. Amino acids can then be combined to make proteins.
  • Breaking down excess proteins to form urea, which is excreted in urine.
  • Converting glucose into starch (plants), glycogen (animals) and cellulose (plants).
• Photosynthesis takes place inside chloroplasts found in plants and algae. The reaction is endothermic. The source of this energy is sunlight. This sunlight is trapped by a chemical called chlorophyll inside chloroplasts. It's used to make carbohydrates. Plants and algae are known as producers and form the first level of all food chains.
• Factors affecting the rate of photosynthesis:
• 
  

  Factors affecting the rate of photosynthesis:

  Carbon Dioxide Concentration

  • However, above a certain threshold, further increases in the carbon dioxide concentration do not increase the rate of photosynthesis because another factor (such as light intensity) is limiting the rate of reaction.

  Temperature

  • However, if the temperature is increased to above about 45°C, the enzymes that catalyse (speed-up) the reaction begin to denature (not work anymore).
  • This causes the rate of the reaction to drop sharply until it stops altogether.
• Factors affecting the rate of photosynthesis:

  Light Intensity:

  • However, if the light intensity is increased above a certain threshold, the rate of photosynthesis will not increase because another factor (such as temperature) is limiting the rate of the reaction.


  Chlorophyll concentration
• Factors limiting the rate of photosynthesis:

  Night - Light Intensity

  Micro-Deficient Soil

  • If plants are grown in mineral-deficient (lacking minerals) soil, they may not absorb enough minerals to produce lots of chlorophyll.
  • In this case, chlorophyll concentration can be the limiting factor.

  Winter - temperature

  Warm and bright - co2 concentration
• The glucose produced by photosynthesis is mainly used for respiration in plants. However, it can also be converted into other products:

  • Proteins are needed for cell growth and repair.
  • A source of nitrogen is also needed for glucose to be converted into proteins.
  • Plants get this nitrogen by absorbing nitrate ions (minerals) from soil.

  Starch

  Fats and oils

  Cellulose - strengthen cell walls
• • You can easily investigate the effect of light intensity on the rate of photosynthesis by using an aquatic (lives in water) plant like pondweed.
  • To do this, change the distance between the lamp and the pondweed and count the number of bubbles produced.
  • In this experiment, light intensity is the independent variable and the number of bubbles is the dependent variable.
• inverse square law = 1 over (distance squared)
• Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration. It describes the movement of particles in fluids (liquids and gases). The particles all move randomly. Substances can move in and out of cells across cell membranes via diffusion (e.g CO2, urea).
• Factors affecting diffusion:

  Concentration gradient - bigger the difference in concentration - bigger gradient - faster rate of diffusion

  Membrane Surface area - larger surface area = faster rate of diffusion

  Temperature - hotter = faster
• Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution (high concentration of water) to a concentrated solution (low concentration of water).
• Osmosis practical

  • Cut discs of raw potato and measure their mass.
  • Put discs in different concentrations of sugar or salt solution.
  • After 30 minutes, measure the mass of each disc again.
  • Do the calculation final mass minus the initial mass of each disc.
  • Divide this number by the initial mass and then multiply by 100 to give a percentage change in mass.
  • The concentration in which the potato's mass changed the least is closest to the water concentration of the potato (because the least water has moved into or out of the potato by osmosis).
• • Active transport allows sugar molecules, which are needed for cell respiration, to be absorbed into the blood from the gut, even when the sugar concentration of the blood is higher.
  • Active transport in the root hairs of plants allows plants to absorb mineral ions, which are necessary for healthy growth, even though the concentration of minerals is usually lower in the soil than in the root hair.


  Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy to accomplish the movement.
• Multicellular organisms cannot rely on diffusion to reach all their cells so they have specialised surfaces. Exchange surfaces are surfaces that are adapted to maximise the efficiency of gas and solute exchange across them. They have the following adaptations:

  Blood supply - These blood vessels replenish

  the blood supply. They do this to maintain a high concentration gradient by bringing in new blood as diffusion starts to even out the concentrations.
• Large surface area - allows for more of a substance to diffuse

  Thin membrane - reduces diffusion distance

  Ventilation - maintain a high conc. gradient
• Examples of exchange surfaces:

  Small intestine - exchanging nutrients between digested food

  Lungs - exchanging oxygen and carbon dioxide

  Gills - oxygen in water and carbon dioxide in the fish's bloodstream

  Roots - water and minerals

  Leaves - exchanging oxygen and carbon dioxide
• The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes. In body cells, the chromosomes are normally found in pairs.

  Chromosomes, present in cell nuclei, are made up of many different genes that encode (produce) many different proteins.