Biology paper 2

• Photosynthesis


  • Takes place inside chloroplasts
  • Endothermic (needs energy) (Sunlight)
  • Sunlight trapped by chlorophyll, makes carbohydrates
  • Plants and algae are producers
• Photosynthesis


  1. Carbon dioxide + water

  2. Glucose + oxygen
• Factors affecting photosynthesis


  • Carbon dioxide concentration
  • Chlorophyll concentration
  • Temperature
  • Light intensity
• Limiting factors


  • Winter? temperature
  • Night? light intensity
  • Mineral-deficient soil? Chlorophyll concentration
• Practical effect of light intensity on rate of photosynthesis

  1. Put pondweed in water

  2. Change the distance between lamp & pondweed

  3. Count bubbles (full of oxygen)
• Inverse square law

  Light intensity = 1 / distance squared
• Uses of glucose


  • Respiration
  • Making starch/fat to store energy
  • Making cell walls
  • More amino acids for proteins
• Transpiration


  Unlike water transport (transpiration), translocation is bidirectional
• Root hair cells


  • Long projections, increases surface area to absorb minerals and nutrients
  • No chloroplasts, (no light for photosynthesis)
  • Transport water up stem to leaves
• Xylem cells


  • Tubes are hollow for water transport
  • Connected dead cells
  • End walls of the dead cells are broken so water moves through
  • Lignin strengthens cell wall
• Stomata


  • Gaps on outer layer of leaf that allow diffusion of gas, including evaporated water in and out of leaf
  • Guard cells open and close stomata
• Opening of stomata


  Guard cells open stomata by taking up lots of water, causing them to swell
• Closing of stomata


  Guard cells lose water, return to limp state
• State of stomata


  • Abundant water? Can afford to lose so opens to allow gas for photosynthesis to move freely in and out
  • Scarce water? Closes to prevent water loss
  • Night? Close as no sunlight
• Transpiration


  1. Root hair cells absorb water in soil via osmosis, mineral ions

  2. Xylem: Water + minerals go through xylem vessels up stem to leaves

  3. Leaves: Water evaporates, water vapour diffuses out stomata
• Factors affecting transpiration


  • Increased humidity (more difficult to evaporate, lower rate)
  • Increased temperature (easier to evaporate, higher rate)
  • Increased light intensity (easier to evaporate, higher rate)
  • Increased air flow (carries water away, higher rate)
• Measuring rate of transpiration

  1. Cut shoot

  2. Set up for a potometer

  3. As water is lost through plant's leaves, the air bubble moves in capillary tube

  4. Speed of bubble movement shows rate of water uptake
• Phloem


  • Transports food to where needed
  • Phloem vessels are made up of living cells
  • Small holes to allow food to move up and down
• Translocation


  • Food from photosynthesis is transported from leaves to growing regions
  • Bidirectional, happens in phloem tubes (elongated cells that have holes in cell wall)
• Endocrine glands


  • Testes (testosterone, puberty)
  • Thyroid (thyroxine, regulate metabolism)
  • Pancreas (insulin, glucagon, regulate blood glucose)
  • Adrenal (adrenaline, fight or flight)
  • Pituitary (main, responds to hypothalamus, triggers other glands)
• Endocrine system


  Coordinates body's response using hormones, which are released by glands into blood
• Nervous system


  Rapid response, detected by receptor cells, carried by neurones, acts on precise part, response is very short
• Endocrine system


  Slower response, uses chemical messengers carried by blood, can act on large area, response can be long-lasting
• Negative feedback in thyroid regulation

  1. Hypothalamus produces TRH

  2. This causes the pituitary to release TSH, stimulating thyroxine secretion by thyroid gland

  3. When normal or above, TRH's reduced, dropping TSH and thyroxin levels
• Adrenaline response


  1. Secreted by adrenal glands

  2. Liver converts glycogen to glucose, raising blood sugar

  3. Enlarge lungs' air passages, changes metabolism to boost oxygen delivery

  4. Increases heart rate and blood pressure by vasoconstriction, increased blood flow to brain and muscles
• Menstrual cycle

  1. FSH: released in pituitary gland, causes egg to mature in ovary. Also stimulates oestrogen

  2. Oestrogen: In Ovaries. Thickens uterus lining. Stimulates LH and stops FSH

  3. LH: Pituitary stimulates release of mature egg on day 14 (ovulation)

  4. Progesterone: In ovaries, maintains lining of uterus 14-28 day, stops release of LH and FSH
• Contraception methods


  • Combined pill: oestrogen + progesterone, inhibits FSH production
  • Progesterone-only pill: Thickens mucus, inhibits FSH release
  • Implant: 3 years in arm, releases progesterone
  • Patch: Changed weekly, releases progesterone
  • Injection: Progesterone, 3 month
• Sterilisation


  • Men: Sperm ducts cut so sperm not released
  • Women: Fallopian tubes cut so egg can't reach uterus
• IVF


  1. Eggs are collected after inducing their release

  2. Fertilised in lab with prospective father's sperm

  3. Embryos develop, then placed back into uterus where they embed and grow normally
• The heart


  • Double circulatory system
  • Deoxygenated blood enters vena cava into the right atrium and right ventricle. The Valve prevents back flow. Goes through pulmonary artery to lungs to be oxygenated. This oxygenated blood returns through the pulmonary vein to left atrium and ventricle and out aorta
  • Left side has thicker walls, higher pressure needed to pump blood to whole body
  • Group of cells in walls of atrium create electrical impulses that cause heart to contract
• Arteries


  • Carry blood away from heart
  • Thick walls and thin lumen to withstand pressure
• Veins


  • Carry blood back to heart
  • Thin walls, wide lumen
  • Valves to prevent backflow
• Capillaries


  Arteries split to capillaries, which have thin walls to allow fast diffusion between blood and cells
• Heart needs supply of oxygen by coronary arteries
• Cardiovascular disease

  Fat builds up in arteries, restricting blood flow
• Stents


  Inserted to open blocked blood vessels
• Statins


  Reduce fatty deposits in arteries
• Blood


  • Carries red and white blood cells, and platelets to clot
• Oxygen


  Dissolves in plasma, binds to haemoglobin in red blood cells for transport
• Carbon dioxide


  Dissolves into plasma, diffuses into lungs to be exhaled