Biology Notes for IGCSE 2014
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    • All Notes
    • 01 Classification
    • 02 Cells
    • 03 Enzymes
    • 04 Plant Nutrition
    • 05 Animal Nutrition
    • 06 Plant transport
    • 07 Human transport
    • 08 Respiration
    • 09 Coordination
    • 10 Excretion
    • 11 Homeostasis
    • 12 Reproduction
    • 13 Inheritance
    • 14 Ecosystem
  • Classification
    • Summary
    • Characteristics of Living organisms
    • Classification of Living organisms
    • Kingdoms of Living organisms
    • Animal Kingdom >
      • Classification
      • Phylum Vetebrates
      • Phylum Arthropods
      • Annelids, Nematodes, Molluscs
    • Plant Kingdom
    • Virus
    • Bacteria Kingdom
    • Fungi Kingdom
    • Dichotomous keys
  • Cells
    • Summary
    • Structure
    • Functions
    • Tissues, Organs, Systems
    • Diffusion
    • Osmosis
    • Active transport
  • Enzymes
    • Summary
    • Enzymes and reactions
    • 'Lock and Key' model
    • Role in germinating seeds
    • Use in biological washing powders
    • Use in the food industry
    • Use of microorganisms and fermenter to manufacture enzymes
    • Use of microorganisms to manufacture antibiotic penicillin
  • Nutrition
    • Animal >
      • Summary
      • 1 >
        • Main nutrients: carbohydrates, fats and proteins
        • Food tests >
          • Food test 1 - Starch test
          • Food test 2 - Benedict's test for Reducing Sugars
          • Food test 3 - Emulsion (ethanol) test for Fats
          • Food test 4 - Biuret test for Proteins
        • Other Nutrients: Vitamins, Minerals, Fiber and Water
        • Using yeast to make bread and beer
        • Using microorganism in making yoghurt and single cell protein
        • Food additives - uses, benefits and health hazards
        • Use of modern technology for increasing food production
      • 2 >
        • Problems of world food supplies and the causes of famine
        • Diet
        • Human alimentary canal
        • Human teeth and dental decay
        • Adding fluoride to public water supplies
        • Mechanical and chemical digestion
        • Absorption – function of the small intestine and significance of villi
        • Assimilation and role of the liver
    • Plant >
      • Summary
      • The equation for photosynthesis
      • Photosynthesis investigations - Principles and Starch test
      • Effect of Light intensity on the rate of Photosynthesis
      • Effect of Temperature on the Rate of Photosynthesis
      • Effect of Carbon Dioxide on the Rate of Photosynthesis
      • Limiting factors in photosynthesis
      • Optimum conditions for photosynthesis in Green house
      • Leaf structure
      • Plant's mineral requirements and fertilisers
  • Transport
    • Plant >
      • Summary
      • Functions of xylem and phloem
      • Distribution of Xylem and Phloem in roots, stems and leaves
      • Root hairs and water uptake by plants
      • Passage of water through root, stem and leaf
      • Transpiration in plants and factors affecting tranpiration rate
      • Adaptations of the leaf, stem and root to different environments
      • Translocation of organic foods in plants
      • Translocation of applied chemicals throughout the plant
      • Transport of materials from sources to sinks at different seasons
    • Human >
      • Summary
      • 1 >
        • The circulatory system
        • Structure and function of the heart
        • Effect of exercise on heartbeat and causes of a coronary heart disease
        • Arteries, veins and capillaries - structure and functions
        • Blood composition and Plasma
        • Blood cells - structure and functions
      • 2 >
        • Blood clotting
        • Immune system - antibody, tissue rejection
        • Functions of lymphatic system
        • Respiration
        • Aerobic and anaerobic respiration
        • Gaseous exchange
  • Respiration
    • Summary
    • Definition
    • Aerobic, anaerobic
    • Gaseous exchange
    • Inspired, expired air
    • Tobacco smoke
  • Reproduction
    • Summary
    • Types
    • Plant >
      • Pollination
      • Flower structure
      • Formation of seed
      • Seed dispersal
      • Self-pollination, cross-pollination
      • Growth and development
    • Human >
      • Reproductive system
      • Menstrual cycle
      • Fertilisation
      • Fetus development
      • Birth
      • Sex hormones
      • Birth control
      • Artificial insemination
      • HIV/AIDS
      • Gonorrhoea
      • Breast feeding
  • Coordination
    • Coordination >
      • Summary
      • Hormones, adrenaline
      • Hormones in food production
      • Human nervous system
      • Simple reflex arc
      • Effectors, biceps and triceps
      • Voluntary, involuntary actions
      • The eye, rods and cones
      • Accommodation
      • Tropism in plants
      • Auxins
    • Homeostasis >
      • Summary
      • Homeostasis
      • Blood glucose
      • Negative feedback
      • Kidney structure
      • Kidney function
      • Formation of urea
      • Dialysis
      • Drugs
  • Inheritance
    • Summary
    • Key definitions
    • Chromosomes, DNA
    • Mitosis and Meiosis
    • Monohybrid cross
    • Codominance
    • Continuous, discontinous
    • Mutation, radiation
    • Sickle cell anaemia
    • Selection
    • Antibiotic-resistance bacteria
    • Genetic engineering
  • Ecosystem
    • Summary
    • Human & ecosystem >
      • Human influences
      • Deforestation
      • Water pollution
      • Air pollution
      • Greenhouse gases
      • Pesticides, nuclear fallout
      • Conservation, recycling sewage
    • Energy flow
    • Food chain
    • Food web
    • Food pyramids
    • Energy efficiency
    • Carbon & water cycles
    • Nitrogen cycle
    • Combustion of fossil fuels
    • Population size

# 56 Absorbtion – function of the small intestine
 and significance of villi

Absorption is the movement of digested food molecules through the wall of the intestine into the blood or lymph. 
Picture
Digestion is completed in the small intestine. By now, most carbohydrates have been broken down to simple sugar, proteins to amino acids, and fats to fatty acids and glycerol. These molecules are small enough to pass through the wall of the small intestine and into the blood. This is called absorption.
Picture
Absorption is movement of digested food molecules through the wall of the intestine into the blood or lymph. The small intestine is especially adapted to allow absorption to take place very efficiently. It has a very rich blood supply. Digested food molecules are small enough to pass through the wall of the intestine into the bloodstream.

Picture
Water, minerals salts and vitamins are also absorbed in the small intestine. The small intestine absorbs 5-10 dm3 of water each day. How ever, the colon absorbs much less water and salt than the small intestine, generally around 0,3–0,5 dm3 per day.
Picture
Significance of Villii 

Villi are finger like projections that increase the surface area for absorption. If a section of small intestine was turned inside out, its surface would be kike a carpet. Inside each villus are:
- Blood capillaries: absorb amino acids and glucose.
- Lacteals: absorb fatty acids and glycerol.
Picture
Food molecules are absorbed:

 - mainly by diffusion.
 - or by active transport.

Epithelial cells contain mitochondria to provide energy for absorption against the concentration gradient.
Picture
Role of the hepatic portal vein 

The hepatic portal vein transports absorbed food from the small intestine to the liver. After a meal, the blood in this vein contains very high concentrations of glucose and amino acids, as well as vitamins and minerals. The liver reduces levels backs to normal. 



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