Biology (B2)

Biology (B2)

1. B2.1 - Cells, tissues and organs

   • Animal and plant cells
     • Human cells
       • Use this acronym to remember what is in a human cell: Nice Chicken Curry Mild Rice
       • Nucleus
         • Controls the cell's activities
       • Cytoplasm
         • Many chemical reactions take place.
       • Cell membrane
         • Controls the movement of materials in and out of cell.
       • Mitochondria
         • Energy is released during aerobic respiration
       • Ribosomes
         • Protein synthesis takes place
     • Plant cells
       • Contain all the things in a human cell, with these extra:
       • Cell wall
         • Made of cellulose for support
       • Chloroplasts
         • Contain chlorophyll for photosynthesis. The light energy is absorbed to make food.
       • Permanent vacuole
         • Contains cell sap
   • Bacteria and yeast
     • -Very small and can only be seen by a microscope.
     • Bacteria
       • Contains a cell membrane and cytoplasm surrounded by a cell wall.
       • NO NUCLEUS - genetic material is in the cytoplasm
       • Multiplied bacteria = bacterial colony
     • Yeast
       • -SINGLE-CELLED organism -Have a nucleus, cytoplasm and a membrane surrounded by a cell wall.
   • Specialized cells
     • -Cells are specialized to carry out a specific function. -The structure of the cell gives clues as to what it does.
     • Muscle cells
       • Many mitochondria to create a lot of energy.
     • Gland cells
       • Many ribosomes to create a lot of protein.
     • Neurons
       • Specialized to carry impulses from receptors to the CNS.
   • Diffusion
     • The spreading out of the particles of a gas, or of any substance in a solution.
     • Concentration
       • NET MOVEMENT into or out of cells depends on concentration on either side of cell membrane.
       • Difference in concentration between two areas is: CONCENTRATION GRADIENT
     • Increasing diffusion
       • Rate is increased when: -Distance is decreased. -Surface area is increased. -Concentration gradient is increased.
     • Examples
       • Diffusion of oxygen into cells of body from the bloodstream. Due to respiration of cells.
       • Diffusion of carbon dioxide into actively photosynthesizing plant cells.
       • Diffusion of simple sugars and amino acids from gut through cell membranes.
   • Tissues and organs
     • Tissues
       • A tissue is a group of cells with similar structure and function.
       • Animal tissues
         • Muscle tissue - Can contract to bring about movement.
         • Glandular tissue - To produce substances such as enzymes or hormones.
         • Epithelial tissue - Covers some parts of the body.
       • Plant tissues
         • Epidermal tissue - Covers the plant
         • Mesophyll - Can photosynthesize
         • Xylem and phloem - transport substances around the plant.
     • Organs
       • Organs are made of several tissue types.
       • The stomach
         • The stomach is an organ made up of: -Muscular tissue to churn the stomach contents. -Glandular tissue to produce DIGESTIVE JUICES. -Epithelial tissue to cover the outside and the inside of the stomach.
   • Organ systems
     • Groups of organs work together in an organ system.
     • The digestive system
       • The digestive system in humans is adapted to exchange substances with the environment.
       • It includes: -Glands, such as the pancreas and salivary glands which produce digestive juices. -Stomach and small intestine where digestion occurs. -Liver which produces bile. -Small intestine where the absorption of soluble food occurs. -The large intestine where water is absorbed from undigested food, producing faeces. 

2. B2.2 - Organisms in the environment

   • Photosynthesis
     • During photosynthesis, light energy is transferred to chemical energy.
     • Some of the glucose is converted into insoluble starch for storage.
     • Equation
       • Carbon Dioxide + Water → Glucose + Oxygen
       • 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂   
     • Process
       • 1. CO₂ taken in by leaves, water taken in by roots. 2. Chlorophyll traps light energy. 3. Energy is used to convert the CO₂ and H₂0 to C₆H₁₂O₆
     • Testing
       • -Testing leaves with iodine solution, to test for starch.  -Green patches will turn solution blue-black to show starch has been made.
       • Variegated leaves
         • Different patches = difference in chlorophyll. Green = Chlorophyll White = No Chlorophyll
   • Limiting factors
     • 3 limiting factors: -Lack of light -Cold (enzymes slower) -Little carbon dioxide
     • Experiments
       • Independent variable: Concentration of Carbon Dioxide
       • Dependent Variable: Volume of Oxygen produced.
       • Control variables: Light, temperature, type of plant
   • How plants use glucose
     • -Converted into insoluble starch for storage. -Respiration -Converted into lipids  and oils for storage. -Produce cellulose which strengthens cell walls. -Produce proteins.
     • Ions
       • Plant and algal cells need a supply of mineral ions such as: -Nitrate ions to produce protein. --Plants absorb nitrate ions from soil. --Algae absorb nitrate ions from the water in which they live.
   • Making the most out of photosynthesis
     • Plant growers can artificially control the environment to improve plant growth.
     • To improve plant growth, the factors that need to be controlled are: -Light intensity -Temperature -Carbon dioxide levels
   • Organisms in their environment
     • The distribution of organisms is affected by environmental factors.
     • -Temperature -Availability of nutrients -Amount of light -Availability of water -Availability of oxygen -Availability of carbon dioxide
   • Measuring the distribution of organisms
     • Quantitative data is used to describe how physical factors might be affecting the distribution of organisms in a habitat.
     • There are two ways to obtain quantitative data: -Random quantitative sampling using a quadrat. -Sampling along a transect.
     • Quadrat
       • -A square from which may be subdivided into a grid.  -Several quadrats are placed randomly and the thing being investigated is counted in each one. -It can be used to estimate the number of species or plant in a field.
     • Transect
       • -This is not random. A line is marked between two points, and a random quadrat placed every 5 metres along the line. -Supplies a lot of information about:  --Habitat --Organisms in it.
     • Sample size
       • In a large field, enough random quadrats are needed so that the sample is representative of the entire field.

3. B2.3 - Enzymes

   • Proteins, catalysts and enzymes
     • Proteins
       • -Made up of long chains of amino acids. -Long chains are folded to produce specific shapes, which have a specific function.
       • They can be: -Structural components of tissues -Hormones -Antibodies -Catalysts
     • Enzymes
       • -Biological catalysts -Large proteins and the shape is vital for its function. -The 'active site' is the area where other molecules can fit.
       • In a reaction, the substrate can: -Be held in the active site. -Be connected to another molecule. -Be broken down.
       • Enzymes can: -Build large molecules from smaller ones. --Starch from glucose molecules -Change one molecule into another -Break down large molecules into small ones.
   • Factors affecting enzyme action
     • -Reactions take place quicker if it is warmer. --At higher temperatures the molecules move around more quickly and so collide with each other more often, with more energy. (Learn this word for word)
     • -Each enzyme works best at a particular pH value.
     • Denaturing
       • If the temperature gets too hot, the active site CHANGE SHAPE, causing the enzyme to stop working.
       • If the pH is too acidic or too alkaline for the enzyme, the active site could change shape.
   • Digestion
     • -These enzymes are produced in the glands and in the lining of the gut. -Enzymes pass out of the cells and come into contact with food. -Digestion involves the breakdown of large, insoluble molecules into smaller soluble ones.
     • Special enzymes
       • Amylase
         • Produced in the salivary glands, the pancreas and the small intestine.
         • Catalyses the digestion of starch into sugar in mouth and small intestine.
         • Work best when the conditions are slightly alkaline.
       • Protease
         • Produced by the stomach, pancreas and small intestine.
         • Catalyses the breakdown of proteins into amino acids in the stomach and small intestine.
         • Work best when the conditions are acidic.
       • Lipase
         • Produced by the pancreas and small intestine.
         • Catalyses the breakdown of lipids to fatty acids and glycerol.
         • Work best when the conditions are slightly alkaline.
     • Bile
       • -The liver produces bile. -Stored in the gall bladder before being released into the small intestine. -Bile neutralises the acid that was added to food in the stomach. -This provides alkaline conditions in which enzymes in the small intestine work most effectively.
   • Uses
     • Biological detergents
       • -Contain proteases and lipases that digest food stains. -Work at lower temperatures than ordinary washing powders. -Saves energy and money spent on electricity.
     • Baby foods
       • Proteases are used to pre-digest proteins in some baby foods.
     • Fructose syrup
       • -Isomerase is used to convert glucose syrup into fructose syrup.  -Fructose is MUCH SWEETER so less is needed in foods. -Foods are less fattening. 
     • Foods
       • Carbohydrases are used to convert starch into sugar syrup for use in foods.
     • Industry
       • -Used to bring about reactions at normal temperatures and pressures. -Traditional chemical processes require: --Expensive equipment. --A lot of energy (to produce high temperatures and pressures)
   • High-tech enzymes
     • Advantages
       • -Enzymes in biological washing powders are very effective at removing stains. -Biological washing powders can be used at lower temperatures. -Used in medicine to diagnose, control or cure disease. -Industry, costs of equipment and energy can be reduced.
     • Disadvantages
       • -Misuse of washing powders can cause allergic reactions on skin. -Enzymes may enter waterways via the sewage system. -Industrial enzymes are costly. -Enzymes denature at high temperatures needed to kill pathogens in the washing. -Fabrics such a wool are digested by proteases.

4. B2.4 - Energy from respiration

   • Aerobic respiration
     • -Takes place continually. -Chemical reactions take place in the mitochondria and are controlled by enzymes.
     • Equation
       • Glucose + oxygen  → Carbon dioxide + water [+ energy]
     • Uses
       • Energy released used to: -Build larger molecules. -Enable muscle contraction. -Maintain a constant body temperature in colder surroundings. -Build sugars, nitrates and other nutrients into amino acids and then proteins in plants.
     • Experiment
       • -Measure volume of carbon dioxide produced.
   • Effect of exercise on the body
     • -During exercise muscles need more energy. -More glucose and oxygen need to be transported to the muscles.
     • Heart rate
       • Increase and the blood vessels dilate to allow more blood containing oxygen and glucose to reach the muscles.
     • Breathing
       • Increase in breathing rate and depth of each breath to allow a greater uptake of oxygen and release of carbon dioxide in the lungs.
     • Glycogen
       • Muscles store glucose at glycogen which can be converted back to glucose during exercise.
   • Anaerobic respiration
     • When muscles work hard for a long time, they may have too little oxygen and become fatigued.
     • Muscles use anaerobic respiration if they are short of oxygen.
     • Anaerobic respiration doesn't break down glucose fully, therefore less energy is released from the glucose.
     • Equation
       • glucose → lactic acid (+ energy released)
     • Oxygen debt
       • In anaerobic respiration, lactic acid replaces carbon dioxide and water as the waste product.
       • When the exercise is complete, the lactic acid MUST be broken down.
       • The extra oxygen you need to oxidize the lactic acid into carbon dioxide and water is called oxygen debt.

5. B2.5 - Simple inheritance in animals and plants

   • Cell division
     • Necessary for the growth of an organism, or for the repair of damaged tissues.
     • Mitosis
       • Two identical cells being produced from the original cell. Mitosis = Making Identical Two
       • Two identical cells being produced from the original cell. 46 chromosomes (2 sets) Mitosis = Making Identical Two
       • Chromosomes
         • Found in pairs and contain genes (alleles) which must be passed onto each new cell.
       • Process
         • -Normal body cell has 46 chromosomes (23 pairs). -Copies of these pairs are made. -Then the cell divides once to form two genetically identical body cells.
     • Meiosis
       • -Cells in reproductive organs divide by meiosis to form gametes.  -23 chromosomes (one set) -Meiosis = Making Eggs
       • Process
         • -Before division, a copy of each chromosome is made. -The cell now divides twice to form four gametes. -Each gamete has a single set of chromosomes with a different combination of genes. 
       • Sexual reproduction
         • -Results in variation as the gametes from each parent fuse. -Half genetic information from mother, half from father. -In fertilization, a single body cell with new pairs of chromosomes form. -Individual develops through mitosis. 
     • Differentiation
       • Most animal cells differentiate early in development and cell division is mainly for: -Repair -Replacement
       • Plant cells can differentiate throughout the life of the plant as it continues to grow.
     • Asexual
       • Asexual reproduction cells are produced by mitosis from the parent cell. They contain the SAME alleles as the parents.
   • Stem cells
     • -Unspecialised. -Found in human embryo and bone marrow. -Differentiate into different types of body cell. -Adult bone marrow stem cells - can differentiate into blood cells.-Hoped that stem cells could be used to cure diseases.
     • Embryos
       • Embryonic stem cells can be used in medical research and treatments.
       • Found: -Spare embryos from IVF. -Created from adult cells. -Taken from the umbilical cord of newborn babies.
       • Issues
         • Economical
           • Very expensive to carry out research using embryonic cells.
         • Ethical
           • -The research is experimental. -Embryos have potential to become a baby and are destroyed. -Embryo cannot give permission.
       • Embryo screening
         • Involves tests to diagnose disorders before the baby is born.
         • Results
           • -Sometimes parents decide to terminate the pregnancy. -Others decide it isn't ethical and keep the baby.
           • In IVF, only healthy embryos are implanted into the mother. Embryos carring FAULTY genes are destroyed, which isn't ethical.
   • Mendel to DNA
     • A monk who worked out how characteristics were inherited.
     • Genes
       • -Found on chromosomes. -Control our characteristics. -Short section of DNA.
       • Genetic code
         • Each genes codes for a particular combination of amino acids which make a specific protein.
     • DNA
       • -A very long molecule with a double helix structure (chromosomes). -Every individual (bar identical twins) has different DNA.
       • DNA Fingerprint
         • Unique DNA pattern which can be used to identify people.
   • Inheritance
     • Sex chromosomes
       • Male
         • An X and a Y chromosome (XY)
       • Female
         • Two X chromosomes (XX)
     • Alleles
       • Genes controlling the same characteristic.
       • Dominent
         • 'Masks' the effect of another allele.
       • Recessive
         • The dominant allele 'masks' this allele, so it has no effect.
     • Genetic diagrams
       • Biological models which can be constructed to predict and explain the inheritance of particular characteristics.
       • Terminology
         • Phenotype
           • Physical appearance of the characteristic (dimples or no dimples)
         • Genotype
           • The genetic make-up, which alleles does the individual inherit.  (DD, Dd, dd)
         • Homozygous
           • Both alleles are the same DD (homozygous dominant) or dd (homozygous recessive).
         • Heterozygous
           • The two alleles are different, Dd.
     • Genetic disorders
       • If an allele is recessive, the person must inherit two recessive alleles to have the disorder.
       • If the allele is dominant, the person has to inherit only one dominant allele to have the disorder.
       • Polydactyly
         • -Caused by a dominant allele. -Where a baby is born with extra fingers or toes.
       • Cystic fibrosis
         • -Caused by a recessive allele. -Affects cell membranes and causes the production of thick sticky mucus. 
       • Carriers
         • People who carry a recessive allele.
     • Punnet squares
       • Used to predict the chances of inheriting a disorder.

6. B2.6 - Old and new species

   • The origins of life on Earth
     • -Believed that the Earth is 4500 million years old and that life began about 3500 million years ago. -There is DEBATE as to whether first live developed due to conditions on Earth, or whether simple life forms arrived from another planet.
     • Fossils
       • -Fossils are remains of organisms from many years ago which are found in rocks. -We can learn from fossils how different organisms have changed as life developed on Earth.
       • -The fossil record is INCOMPLETE.
       • How they are formed
         • -From hard parts of animals that do not decay easily (teeth, claws) -From parts of organisms that have not decayed because some of the conditions for decay are absent (ice preservation). -When parts of the organism are replaced by other materials, such as minerals, as they decay. -As preserved traces of organisms (footprints, burrows).
       • Destruction
         • Traces which were left are likely to have been destroyed by geological activity such as earthquakes.
       • Soft-bodied
         • Soft-bodied organisms didn't leave fossils.
   • Exploring fossil evidence
     • -The fossil record is incomplete. -We can learn a lot from fossils which exist. -Some organisms have changed a lot over time. -Other have changed very little. -Some have become extinct.
     • Extinction
       • A species which once existed has completely died out. 
       • Factors
         • -A new disease may kill all members of a species. -Change in environment. -New diseases may be introduced. -A new predator may evolve or be introduced to an area that kills and eats all of a species. -A new competitor - original species may be left with little or nothing to eat. -A single catastrophic event may occur which destroys the habitat. -Natural changes in species occur over time.
   • More about extinction
     • The biggest influences on a species survival are changes in the environment.
     • Climate change
       • -A species which is very well adapted to a hot climate may become extinct in an Ice Age. -There could be insufficient food or it is too cold to breed.
       • -Climate change may: --Make it too cold or hot. --Make it too wet or dry. --Reduce a species food supply.
     • Fossil evidence
       • -Shows that there have been mass extinctions on a global scale. -Many of the species died out over a period of several million years - a short time.
       • -The habitat the species live in may be destroyed by catastrophic events such as a major volcanic eruption. -The environment can change dramatically following a collision between a giant asteroid and Earth.
     • The dinosaurs
       • No one knows why they have become extinct. Some ideas are: -The collision of a giant asteroid caused huge fires, earthquakes, landslides and tsunamis. The dust which rose blocked out the sun, lowering temperatures and causing darkness. Plants could not grow. -The extinction was a slower process due to sea ice melting and cooling the sea temperature by 9 degrees, therefore there was less plankton - less food available. 
   • Isolation and the evolution of new species
     • New species can arise form existing species if a group becomes isolated from the rest.
     • Geographical isolation
       • -Could occur if an island separates from the mainland or if a new river separates two areas. -Mountain ranges and old craters can isolate organisms. 
     • Speciation
       • Logical process: Isolation → Genetic variation → alleles selected → interbreeding no longer possible → new species (speciation).
       • Isolation
         • New species can occur following separation of two populations, as in geographical isolation. 
         • Genetic variation
           • Each population has a wide range of alleles that control their characteristics.
           • Natural selection
             • -Occurs in both populations. -The alleles that control the characteristics which help the organism to survive are selected. -The organisms with these alleles will survive and breed.
             • Evolution
               • If the environment, competitors, food supply and predators are different for each population, they will evolve differently. 
               • Interbreeding
                 • SPECIATION has occurred when the two populations can no longer successfully interbreed.

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