bio 2e edexcel igcse

• photosynthesis

  water + carbon dioxide ==(light)==> glucose + oxygen

  affected by:

  • temperature
  • carbon dioxide concentration
  • light intensity (LI = 1/d^2)
• investigating photosynthesis

  • set up an aquatic plant (eg pondweed) and count bubbles over a set time period (eg 1 minute)
  • use led lamp as it wont raise the water temperature
  • sometimes sodium hydrogen carbonate is added to supply carbon dioxide
  • light intensity: vary lamp distance/brightness
  • carbon dioxide: vary concentration of sodium hydrogen carbonate
  • temperature: vary in water bath
• investigating starch production

  • cover half of a leaf with paper or foil or use a variegated leaf
  • place plant in sunlight over 48 hours
  • boil leaf in water to preserve, kill and soften it.
  • put leaf in hot ethanol for 10 minute to remove chlorophyll pigment
  • put leaf in petri dish with iodine solution
  • covered half will remain orange-brown, uncovered half will turn blue-black, as the iodine changes in the presence of starch
• the leaf part functions

  • waxy cuticle: reduces water loss by evaporation and acts as a protective layer at the top of the leaf
  • upper epidermis: very thin and transparent to let in light for the palisade mesophyll
  • palisade mesophyll: contains lots of chloroplasts for rapid photosynthesis
  • spongy mesophyll: has a lot of air spaces to allow faster diffusion between cells, bc increases the sa:v ratio
  • lower epidermis: contains guard cells and stomata
  • guard cell: cells that open and close the stomata by absorbing or losing water. when turgid, stomata opens
  • stomata: where gas exchange takes place.
• general: hypertonic - isotonic - hypotonic

  plant: plasmolyzed - flaccid - turgid

  animal: shrivelled - normal - lysed
• mineral ions

  ---- magnesium:

  • required for chlorophyll production
  • deficiency causes leaves to turn yellow

  ---- nitrate:

  • required for amino acid production
  • deficiency causes leaves to turn yellow and stunted growth
• functions of nutrition in humans:

  • carbohydrates: high energy source
  • proteins: growth and repair
  • lipids: high energy source for insulation
  • dietary fibre: roughage to keep food moving through gut. deficiency causes constipation
  • vitamin a: vision and growth
  • vitamin c: absorbing iron
  • vitamin d: absorbing calcium
  • calcium: bone and teeth strength. deficiency causes rickets, curves bones
  • iron: haemoglobin. deficiency causes anaemia
  • water: enables cell reactions
• examples of nutrition in humans:

  • carbohydrates: bread, rice, potato
  • proteins: meat, dairy, pulses
  • lipids: butter, oil
  • dietary fibre: vegetables, cereal grain
  • vitamin a: carrots, green vegetables
  • vitamin c: citrus, broccoli, peppers
  • vitamin d: margarine, oily fish
  • calcium: milk
  • iron: red meat
• factors affecting energy requirements

  • increases and decreases with age, peaking at adulthood
  • activity
  • pregnancy, to support growth and carrying extra mass of baby
• digestion- mouth

  • mechanical digestion: teeth chew food to break it up, increases sa:v ratio
  • chemical digestion: salivary glands produce saliva with amylase in it, which breaks down starch into glucose
• peristalsis is the movement of food due to unidirectional contractions of a tube created by circular and longitudinal muscles.
• digestion- oesophagus

  • tube that carries food bolus (chewed food) from mouth to stomach by peristalsis
• digestion- pancreas

  • produces carbohydrase, lipase and protease enzyme
  • secretes enzymes into stomach and small intestine
• digestion- stomach

  • gastric juice released from stomach lining when food is detected in the stomach
  • this is made of pepsin (an enzyme that breaks down proteins) and hydrochloric acid (makes stomach acidic enough for pepsin to function optimally, and to kill any ingested bacteria)
  • peristalsis occurs here
  • digested food at this stage is called chyme
• digestion- duodenum

  • first part of the small intestine
  • carbohydrases, proteases and lipases digest food here
  • bile is produced in the liver, and stored in the gallbladder, before being released here. this is alkaline to neutralise the acid from the stomach, as these enzymes have a higher optimum pH. it also emulsifies fat (breaks down into small pieces.) the larger surface enables lipids to break down faster.
  • peristalsis occurs here.
• digestion- ileum

  • second part of the small intestine
  • lined with villi, which have a thin lining, a large capillary network and large surface area to absorb soluble molecules into the blood.
• digestion- large intestine

  • water absorbed here to produce faeces, which is stored in the rectum and excreted through the anus
• digestive enzymes

  • starch ==(amylase, a carbohydrase)==> maltose
  • maltose ==(maltase, a carbohydrase)==> glucose
  • proteins ==(protease)==> amino acids
  • lipids ==(lipase)==> glycerol and 3 fatty acids
• investigating the energy content of a food sample (calorimetry)

  1. pour cold water into a boiling tube
  2. record starting temperature with thermometer
  3. record mass of food sample with mass balance
  4. heat sample on bunsen burner till it catches fire using needle to hold
  5. put sample beneath test tube
  6. record final temperature once sample stops burning
  7. Q=mcAT if c = 4.2 J/gC and AT is temperature difference (A is delta)