Presentation on theme: "B2 Revision 2012 Specification. All living things are made up of cells. The structures of different types of cells are related to their functions."— Presentation transcript:
B2 Revision 2012 Specification
All living things are made up of cells. The structures of different types of cells are related to their functions.
PartFunction Nucleus Contains genetic material, which controls the activities of the cell Cytoplasm Most chemical processes take place here, controlled by enzymes Cell membrane Controls the movement of substances into and out of the cell MitochondriaMost energy is released by respiration here RibosomesProtein synthesis happens here Parts of cells which animal and plant cells have in common:
PartFunction Cell wallStrengthens the cell Chloroplasts Contain chlorophyll, which absorbs light energy for photosynthesis Permanent vacuole Filled with cell sap to help keep the cell turgid Parts of cells which only plant and algal cells contain:
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 specialised for a particular function. Their structure will allow them to carry this function out. CellJobAdaptations Leaf cell: absorbs light for photosynthesis lots of chloroplasts Root hair cell: absorbs water and mineral ions finger like shape for large surface area Sperm cell: fertilises an egg head contains an enzyme to help penetrate egg Red blood cell: carries oxygen to the cells thin outer membrane so oxygen diffuses easily
Substances have to pass through the cell membrane to get into or out of a cell. Diffusion is a process that allows this to happen. Particles diffuse from 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 TissueFunction Muscular tissueContracts, bringing about movement Glandular tissue Produces substances such as enzymes and hormones Epithelial tissueCovers some parts of the body
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.
Leaves are adapted to absorb sunlight for photosynthesis
Three factors can limit the speed of photosynthesis: light intensity carbon dioxide concentration temperature
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 oxygen and 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? The enzyme is the lock, and the reactant is the key. enzyme reactant + enzyme-reactant complex ↔ products enzyme + ↔ + ↔↔ +
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. Activation energy: 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 37 o C. Over 40 o C 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 starch into sugars. It works in the mouth and small intestine.
Protease Made in the stomach, pancreas and small intestine. It breaks down protein into 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 enzymes made in the pancreas and small intestine work best in alkaline conditions. The liver produces bile which is released into the small intestine. Bile neutralises the acid that was added to the food in the stomach.
IndustryFunction of enzymes confectionery (sweets) change glucose into fructose, which is sweeter so less is needed and is used in 'slimming' foods (isomerase). baby foodstart off digestion of food (proteases and lipases) biological detergent break down stains (proteases and lipases). What do enzymes do for us?
Mitochondria: tiny organelles found in most plant and animal cells. Where the respiration reactions 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: Oxygen and glucose must be delivered to them more quickly Waste carbon dioxide must be removed more quickly This is achieved by increasing: depth of breathing rate of breathing heart rate
Inside each cell is a nucleus. Inside the human nucleus are 46 chromosomes (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. Where is the genetic information in a cell?
The genetic material is copied The cell divides once to form two genetically identical body cells Mitosis is used for growth or to replace cells. Mitosis
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 cords and bone marrow. There are social and 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 chromosomes in 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 genotypes produced when two organisms breed.
Evolution 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. 60 million years ago 1 million years ago
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
Why did the dinosaurs become extinct? Volcanoes Rocks formed by huge eruptions 65 million years ago can be found in India today. Meteorite Impact The remains of a 180km-wide crater caused by a meteorite 65 million years ago can be found near Mexico. Disease This theory doesn’t explain why so many sea animals died at the same time.