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B2 Revision. 2012 Specification. All living things are made up of cells. The structures of different types of cells are related to their functions. . Parts of cells which animal and plant cells have in common:. Parts of cells which only plant and algal cells contain:.
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B2 Revision 2012 Specification
All living things are made up of cells. The structures of different types of cells are related to their functions.
Bacteria are single celled organisms which contain: cytoplasm cell membrane cell wall no distinct nucleus
Yeast is a single-celled organism, similar to bacteria, containing: • Cytoplasm • Cell membrane • Cell wall But, they also have a nucleus.
Cells may be specialisedfor a particular function. Their structure will allow them to carry this function out.
Substances have to pass through the cell membrane to get into or out of a cell. Diffusionis a process that allows this to happen. Particles diffusefrom an area of high concentration to an area of low concentration.
Diffusion happens in our: • Gut: digested food particles diffuse from the gut cavity to blood in the villus • Lungs: oxygen moves from the alveoli into capillaries around the lungs
A tissue is a group of specialised cells that have a similar structure and function. cells tissues organs organ systems
Organ systems are groups of organs that carry out a particular function. For example, the digestive system:
Plants also usually contain differentiated cells, tissues and organs.
Three factors can limit the speed of photosynthesis: • light intensity • carbon dioxide concentration • temperature
Farmers can use their knowledge of limiting factors on photosynthesisto increasecrop yields. • Artificial light – extends time for photosynthesis • Heating – increases the rate of photosynthesis • Adding carbon dioxide (CO2) – increases the rate Think about economics: The cost of providing extra lighting, heat and carbon dioxide has to be weighed against the increased crop yield and the extra income it will provide. Tip: paraffin lamps provide light, heat and CO2!
Glucose is produced during photosynthesis and is used by the plant to make: • Cellulose - which strengthens the cell wall • Proteins - such as enzymes and chlorophyll Glucose is stored by plants as starch, fats and oils. Plants also need nitrates to do this
The distribution of living organisms in a particular habitat may be affected by physical factors, such as: • Temperature • Amount of light • Availability of water • Availability of nutrients • Availability of oxygenand carbon dioxide
Sampling: Quadrat • Square frame • Used to sample a small area • Samples chosen at random
Sampling: Along a Transect • Not random • Tape stretched between two points • Samples taken along the line using a quadrat • Shows how the distribution of organisms changes along the line
Enzymes • Biological catalysts: speed up reactions. • Enzymes are protein molecules, and so are made up of amino acids.
What happens at the active site? + + enzyme enzyme ↔ enzyme-reactant complex ↔ + + reactant products The enzyme is the lock, and the reactant is the key. ↔ ↔
+ Key phrases: Catalyst: A substance which changes the rate of a chemical reaction without being changed itself. Enzyme: A biological catalyst. Active site: Where substrates bind to an enzyme and undergo a chemical reaction. Activationenergy: The minimum amount of energy particles must have to be able to react.
Temperature and enzymes Most enzymes in the human body work best at about 37oC. Over40oC most enzymes will stop working. The amino acids they are made form start to unravel and the shape of the active site changes. We say that the enzyme is denatured.
pH and enzymes Changes in pH alter an enzyme’s shape. The best pH for an enzyme depends on where it normally works. For example, intestinal enzymes have an optimum pH of about 7.5 (alkaline). Enzymes in the stomach have an optimum pH of about 2 (acidic).
Amylase Made in the salivary glands, pancreas and small intestine. It breaks down starchinto sugars. It works in the mouth and small intestine.
Protease Made in the stomach, pancreas and small intestine. It breaks down proteininto amino acids. It works in the stomach and small intestine.
Lipase Made in the pancreas and small intestine. It breaks down lipids (fats and oils) into fatty acids and glycerol. It works in the small intestine.
The enzymesmade in the pancreasand small intestinework best in alkaline conditions. The liverproduces bilewhich is released into the small intestine. Bile neutralises the acid that was added to the food in the stomach.
Mitochondria: tiny organellesfound in most plant and animal cells. Where the respirationreactions happen. More active cells have more mitochondria.
Aerobic respiration (with oxygen) glucose + oxygen → carbon dioxide + water (+ energy) When too little oxygen reaches the muscles during exercise, they use anaerobic respiration to obtain energy. Anaerobic respiration (without oxygen) glucose → lactic acid (+ energy)
During exercise, the muscle cells respire more than they do at rest. This means that: • Oxygenand glucose must be deliveredto them more quickly • Waste carbon dioxide must be removed more quickly This is achieved by increasing: depth of breathing rate of breathing heart rate
Where is the genetic information in a cell? • Inside each cell is a nucleus. • Inside the human nucleus are 46chromosomes (two sets of 23, one set from Mum, one set from Dad). • Chromosomes are made from DNA. • A section of DNA is called a gene.
Mitosis • The genetic material is copied • The cell divides once to form two genetically identical body cells • Mitosis is used for growthor to replacecells.
Meiosis Forms gametes (sex cells). The cell divides twice to form four gametes. Each daughter cell contains half of the chromosomes of the original cell.
Stem Cells Unspecialised - they can become any type of cell in the human body. As the cells of an embryo divide (by mitosis) and the embryo develops, the cells become differentiated.
Stem cells can be used in new treatments for Parkinson's disease and paralysis. Can be harvested from inside embryos, umbilical cordsand bone marrow. There are socialand ethical issues concerning the use of human embryonic stem cells.
Plant cells Most plant cells stay unspecialised. They can differentiate all through their lives. Unspecialised cells are made at the stems and roots, where mitosis takes place almost constantly. This makes it very easy to clone plants.
Alleles Different forms of the same gene For example, eye colour
Determining sex Human body cells have 23 pairs of chromosomesin the nucleus. One of these pairs controls the inheritance of gender - whether offspring are male or female.
Dominant or Recessive? Alleles are dominant or recessive.
Punnett Squares Show the possible genotypesproduced when two organisms breed.
Evolution 60 million years ago 1 million years ago Fossils are the remains of organisms which died thousands or millions of years ago. By looking at fossils, we can see that organisms have changed very slowly over time.
Prokaryotes Eukaryotes Multicellular life Animals Land plants Mammals Humans
Fossils form if an organism does not decay because: • little oxygen was present • poisonous gases killed of decay causing organisms • low temperature
Fossil Formation Trace or imprints are left behind by organisms. Isle of Wight, UK
Fossil Formation Hard parts of organism replaced by minerals. This is the most common type of fossil.
The fossil record is incomplete. Why? • Early forms of life were soft bodied. • Fossilisation requires very specific conditions. • Many fossils are destroyed. • Many fossils have not been found yet.
Evolution by Natural Selection Individuals in a species show a wide range of variation. This is because of differences in genes. Individuals most suited to the environment are more likely to survive and reproduce. The successful genes are then passed to the offspring in the next generation. Charles Darwin
Extinction What causes organisms to become extinct? • Competition • New predators • New diseases • Environmental changes
