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OCR Gateway B Module B3: Living and Growing
Chromosomes:
- Are made of DNA
- Carry coded information (genetic code) in the form of genes
- Genetic code controls all activity and consequently some characteristics
Protein synthesis:
- Respiration occurs within mitochondria (in cytoplasm) in the cell and more mitochondria are found in cells where more energy is needed
- Ribosomes are also found in the cytoplasm, these are the site of protein synthesis (when proteins are created). They are too small to see with a light microscope
- The nucleus in cells contains genes, each one codes for a particular protein. Proteins are needed for cell growth/repair
DNA:
- DNA is made of 2 strands in a double helix shape and contains pairs of bases: A pairs with T and C pairs with G. This is known as complimentary base pairing
- These bases code for amino acids. 3 bases code for each amino acid
- DNA cannot leave the nucleus, so each gene is copied - the code is moved to ribosomes by mRNA where more can be created
- DNA was discovered by Watson and Crick in 1953 and won the Nobel prize in 1962, although they used data from other scientists, such as photos and data indicating pairing of bases
Proteins:
- Proteins are long chains of amino acids. Different sequences of amino acids result in differently shaped molecules and different functions
- Some of their functions are structural (eg collagen), hormones (eg insulin), enzymes and carrier protein (eg haemoglobin)
Enzymes:
- Enzymes speed up chemical reactions in the body and are sometimes referred to as biological catalysts
- Some of these reactions that they catalyse are photosynthesis, respiration and protein synthesis
- The molecule that will be catalysed (substrate) fits into the active site of the enzyme (known as a lock and key mechanism). Most enzymes only work on one type of substrate, specificity
- At low temperatures, enzymes work slower because there is less chance of a collision
- At a too high or too low pH or at high temperatures, the active site changes shape and will no longer fit a substrate, called denaturing
- The temperature coefficient (Q10) is calculated as follows:
rate at higher temperature ÷ rate at lower temperature
Mutations of genes:
- Mutations cause variation
- They may occur spontaneously (randomly) but can be caused or sped up by radiation or chemicals
- They may lead to different proteins being produced
- They may have no effect
- They may give the individual an advantage
- Mutations change the order of the four bases
- Some cells produce different proteins to others (some genes are switched off)
Respiration:
- Respiration releases energy from food and energy is trapped in ATP molecules, which can provide energy; for muscle contraction, protein synthesis and control of body temperature
- Aerobic respiration involves oxygen:
C6H12O6 + 6O2 -> 6CO2 + 6H2O
- Anaerobic respiration occurs when muscles don't get enough oxygen:
glucose -> lactic acid (+ energy)
- This lactic acid builds up in the muscle, causing pain and fatigue and is not as efficient (less energy per glucose molecule)
- During recovery, high blood flow takes lactic acid to the liver, which breaks it down
- Respiration is measured by the rate of oxygen or carbon dioxide production
- The respiratory quotient is calculated as follows:
CO2 used ÷ O2 used. For glucose, the respiratory quotient (RQ) is 1
- Metabolic rate is the rate of all reactions in the body. If it's high, more oxygen is needed, so faster aerobic respiration
- Respiration is controlled by enzymes, so it is therefore affected by temperature and pH
Multicellular organisms:
- Multicellular organisms have more than one cell and each may have a different purpose: cell differentiation
- However, this requires complex communication, nutrient distribution and control exchange systems
Mitosis:
- Body cells are diploid and have 2 copies of each chromosome
- Mitosis is used to produce new cells
- All chromosomes are copied: new cells still need 2. All mammals have 2 chromosomes (they're diploid)
- DNA replication involves the two strands 'unzipping' to form single strands, and new double strands forming by bases lining up in complimentary pairings
Meiosis:
- Meosis produces gametes (haploid cells - half the number of chromosomes)
- There are 2 divisions; 4 haploid cells are formed, all genetically different
- Sperm cells have many mitochondria for energy and they release enzymes
Platelets:
- Platelets help the blood to clot
Blood plasma:
- Plasma in the blood carries dissolved food substances (eg glocose), CO2 from tissues, hormones, plasma proteins (eg antibodies) and waste (eg urea)
Red blood cells:
- Red blood cells are small and shaped as biconcave disks for a large surface area. They have no nucleus and contain haemoglobin which combines with oxygen and gives oxygenated blood its red colour
Blood transportation and the heart:
- Arteries carry blood from the heart to tissues. They have an elastic wall for coping with high pressure
- Veins carry blood from tissues back to the heart. There are large valves since the pressure is very low
- Cappillaries link arteries to veins and carry blood to cells. They have permeable walls for substance transfer
- Components of the heart:
- Left and right atria receive blood from veins
- Left and right ventricles pump blood to arteries
- Semilunar, tricuspid and bicuspid values prevent backflow
- Pulmonary veins and the vena cava are main veins to the heart
- The left ventricle has a thicker wall - it pumps blood to the whole body, not just lungs for oxygenisation like the right ventricle
- Humans have a double circulatory system: heart -> lungs -> heart -> body -> [repeats]
Growth:
- Differentiation is the process of cells becoming specialised
- There are two main human growth stages: ages 0-4 and 13-16
- Dry mass is the best growth measure - length only measures one dimension of growth
- Different parts grow at different rates in an organism
- Stem cells stay undifferentiated - they can develop into all types of cell, making them very useful. However, the easiest way to obtain them is from embroyos, which is very controversial
- In plants, the only cell division is in meristems (at the tips of roots/shoots). Instead, the cells enlarge
- Plant cells always keep the ability to differentiate
Bacterial cells compared to plant cells:
- Bacterial cells lack a 'true' nucleus, DNA is in a single circular strand in the cytoplasm instead. They have no mitochondria, or chloroplasts
Parts of a plant cell:
- Vacuole containing sap and providing support
- Cell wall (celluose), providing support
- Cell membrane
- Cytoplasm
- Nucleus
Selective breeding:
- Selective breeding (only breeding animals/plants with desirable characteristics) can cause inbreeding (breeding of very genetically closely related organisms), creating health problems
- Inbreeding reduces allele variety in the gene pool, reducing variation and increasing the risk of harmful recessive characteristics
Genetic engineering:
- Genetic engineering processes: desired characteristics are selected and genes for this are removed. They are inserted into another organism, which is allowed to reproduce
Gene therapy:
- Gene therapy is used to cure certain disorders. It could involve body cells or gametes which is more controversial and could lead to 'designer babies'
The process of cloning (specifically of Dolly the sheep):
- Cloning is an type of asexual reproduction
- Dolly was the first mammal cloned from an adult
- Dolly was produced with nuclear transfer - nucleus to egg
- A nucleus in an egg cell is replaced with the nucleus from the udder cell of the sheep to be cloned
- This is given an electric shock to make it divide
- The embroyo is implanted into a mother sheep
- This will be an exact clone of the sheep who donated the udder cell
- Identical twins are naturally occurring clones
Possible uses of cloning animals (These are all controversial):
- Producing embroyos for stem cells or other human organs
- Mass producing animals with desirable characteristics
Cloning plants:
- Many small pieces of tissue are cut from the plant
- These are grown in a growth medium
- Aseptic technique is used at all stages to reduce the risk of microbes infecting plants
- Cloning plants is a lot easier than cloning animals - plant cells retain the ability to differentiate
- Spider plants, potatoes and strawberries can reproduce asexually
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