Biology Lecture Notes Flashcards

Cells

• All living organisms have the following in common:
  • Movement
  • Respiration
  • Sensitivity
  • Growth
  • Reproduction
  • Excretion
  • Nutrition

Virus

• Structure: Protein coat
• Unicellular or multicellular: N/A
• Pathogenic?: Always
• Examples: HIV, Influenza

Bacteria

• Structure: Cell wall, variable, cell wall, RNA or DNA, NO distinct nucleus, plasmids.
• Unicellular or multicellular: Unicellular
• Pathogenic?: Sometimes
• Examples: Lactobacillus, TB, Pneumococcus

Protoctist

• Structure: Similar to animals, cytoplasm contains a nucleolus, algae or cell membrane.
• Unicellular or multicellular: Unicellular
• Pathogenic?: Sometimes
• Examples: Chlorella, Amoeba, Plasmodium

Fungi

• Structure: Cell wall (chitin), cytoplasm cell membrane, vacuole, a mycelium, hyphae.
• Unicellular or multicellular: Either
• Pathogenic?: Sometimes
• Examples: Mucor, Yeast

Animal Cell

• Respiration occurs in the mitochondria.
• Cytoplasm is a jelly-like substance found inside all cells.
• True. Almost all cells have a nucleus.
• True. Animal cells have cell membranes.
• False. Animal cells have cell walls.
• True. All cells contain some cytoplasm.
• All plant and animal cells have cytoplasm because it is where the cell’s chemical reactions take place.
• There are some differences between animal and plant cells because they need to perform different functions.
• Both plant and animal cells have a cell membrane because it is needed to control what goes in and out of the cell.
• Nearly every type of cell has a nucleus because it contains the instructions that control what the cell does.

Plant Cell

• Photosynthesis - chloroplasts are the location.
• Cell Wall - provides support.
• False. All plant cells contain chloroplasts.
• It contains the instructions that control what the cell does.
• Plant cells contain cellulose which gives the cell shape and supports the plant.
• Animal cells do not have chloroplasts because they are unable to photosynthesise.

Functions of Cell Parts

• Nucleus: Controls the activities of the cell.
• Mitochondria: Site of aerobic respiration.
• Ribosome: Site of protein synthesis.
• Cell membrane: Controls entry and exit of substances.
• Cytoplasm: Where chemical reactions take place.
• Cell wall is made of cellulose.
• Chloroplasts contain chlorophyll, which is needed for photosynthesis.
• Function of the cell wall is to support and protect the cell.
• Nucleus controls the cell’s activities and contains DNA.
• Vacuole contains cell sap, which is mostly water.

Definitions

• Cell: A group of organelles working together to perform the same function.
• Tissue: A group of cells working together to perform the same function.
• Organ: A group of tissues working together to perform the same function.
• Organ System: A group of organs working together to perform the same function.
• Four organ systems within the human body:
  • Reproductive
  • Respiratory
  • Circulatory
  • Nervous
  • Also Digestive, Excretory, Endocrine

Food Tests

• Glucose:
  • Reagent: Benedict's Reagent
  • Method: Heat
  • Positive Result: From blue to brick red
• Starch:
  • Reagent: Iodine solution
  • Method: N/A
  • Positive Result: Brown turns to blue black
• Fat:
  • Reagent: Ethanol
  • Method: Shake
  • Positive Result: Milky white water emulsion
• Protein:
  • Reagent: Biuret Reagent
  • Method: N/A
  • Positive Result: Blue to purple

Enzymes

• Enzymes are made of protein. These are made up of amino acids.
• Enzymes are biological catalysts. They speed up reactions by lowering the activation energy.
• Enzymes have an active site. This is where the substrate joins.
• The active site is complementary and specific to the corresponding substrate.
• Enzymes speed a reaction up but do not change.

Effect of Temperature on Enzyme Activity

• As temperature increases, the enzyme's activity increases. At 37°C, the enzyme's activity is greatest. At temperatures above 37°C, the enzyme's activity decreases.
• At higher temperatures, enzymes and substrates have more kinetic energy. At the optimum temperature, the most enzyme-substrate complexes are formed. At higher temperatures, enzymes denature, the active site changes shape and the substrate no longer fits.
• Optimum temperature is the temperature at which maximum enzyme activity occurs.
• Enzymes are biological catalysts.
• Enzymes speed up the rate of chemical reactions.
• Enzymes are specific because they only work on one substrate.
• The substrate fits into the active site of the surface of the enzyme.
• With an increase in temperature, the rate of reaction increases.
• Enzymes can be re-used, so only small amounts are needed.
• Enzymes belong to the group of chemical compounds called proteins.
• An enzyme is specific for a particular substrate because their active sites are complementary to specific substrates only.
• An enzyme can be used again and again because it is unchanged by a chemical reaction and can be reused.

Enzyme-Controlled Reactions

• A decrease in temperature would cause a decrease in the rate of reaction because enzymes and substrates would have less kinetic energy.
• A lowering of pH would decrease the rate of reaction because the enzyme has been denatured and the active site has changed shape.
• Product: Substance formed from the substrate at the end of a chemical reaction with an enzyme.
• Active Site: Region on the surface of an enzyme that fits the substrate.
• Enzymes: Proteins that speed up a chemical reaction.
• Catalyst: Enzyme. Substance that speeds up a chemical reaction without being changed themselves.
• Substrate: Substance that an enzyme acts upon.
• Activation Energy: The amount of energy required for a chemical reaction to activate.

Digestion

• Amylase:
  • Produced in: Salivary glands, pancreas
  • Breaks down: Starch
  • Products produced: Maltose
• Proteases:
  • Produced in: Stomach, pancreas
  • Breaks down: Proteins
  • Products produced: Amino acids
• Lipases:
  • Produced in: Pancreas
  • Breaks down: Lipids
  • Products produced: Fatty acids, glycerol
• Bile is produced in the liver.
• Bile is stored in the gall bladder.
• Bile works in the small intestine.
• Bile is an alkaline liquid. It neutralises the acidic food from the stomach. It also emulsifies fat, which increases the surface area for enzymes to work upon.
• Two reasons why we have stomach acid:
  • Kills pathogens.
  • Provides optimum pH for protease.

Stomach Protection

• Secretion of mucus from its lining.

Lipase Experiment

• The optimum temperature for lipase is 40°C.
• The indicator colour did not change in test tube 1 because the temperature is too low, and enzymes/substrates have too little kinetic energy.
• The indicator colour did not change in test tube 5 because the temperature is too high, and the enzymes have denatured.
• If test tube 1 was warmed up to 40°C, it would turn yellow as enzymes/substrates have more kinetic energy.
• If test tube 5 was allowed to cool to 40°C, it would stay red as the enzyme has denatured.
• Mouth: Physical digestion by teeth breaks up food to increase the surface area. Amylase digests starch into maltose.
• Stomach: Physical digestion by stomach muscles contracting increases surface area. Protease digests protein into amino acids.
• Small Intestine:
  • Villi and microvilli increase the surface area for absorption.
  • Lacteals allow fat absorption.
  • Thin walls provide a short diffusion distance.
• Bile emulsifies fats and neutralises hydrochloric acid.

Balanced Diet

• A balanced diet includes appropriate proportions of:
  1. Carbohydrates
  2. Proteins
  3. Lipids
  4. Vitamins
  5. Minerals
  6. Water
  7. Fibre
• Protein:
  • Function: Growth and repair of muscles.
  • Food Sources: N/A
  • Deficiency Disease: Kwashiorkor
• Fat:
  • Function: Energy source, insulation.
  • Food Sources: N/A
  • Deficiency Disease: N/A
• Carbohydrates:
  • Function: Energy source.
  • Food Sources: Pasta, rice, bread.
  • Deficiency Disease: N/A
• Vitamin A:
  • Function: Good eyesight.
  • Food Sources: Fish liver oils.
  • Deficiency Disease: Night blindness
• Vitamin C:
  • Function: Sticks cells together.
  • Food Sources: Citrus fruits.
  • Deficiency Disease: Scurvy
• Vitamin D:
  • Function: Strong bones.
  • Food Sources: Fish liver oils, sunlight on skin.
  • Deficiency Disease: Rickets
• Iron:
  • Function: Needed for haemoglobin in red blood cells.
  • Food Sources: Red meat, spinach.
  • Deficiency Disease: Anaemia
• Calcium:
  • Function: Strong teeth and bones.
  • Food Sources: Milk, cheese.
  • Deficiency Disease: N/A

Dietary Explanations

• Scurvy in Sailors: Diets lacking in citrus fruits which contain vitamin C.
• Milk for Children: Contains calcium needed for strong teeth and bones, contains protein needed for growth and repair of muscles.
• Steak for Bodybuilders: Contains protein needed for growth and repair of muscles.
• Large Molecule - Small Building Block
  • Protein - Amino acids
  • Fatty acids & glycerol - Lipids
  • Carbohydrate - Glucose

Diffusion, Osmosis, and Active Transport

• Diffusion: Net movement of particles from an area of high concentration to an area of low concentration.
• Three factors that increase the rate of diffusion:
  • Increased temperature
  • Increased surface area
  • Steeper concentration gradient
• (i) Movement of oxygen molecules: A
• (ii) Movement of carbon dioxide molecules: B
• Name of the process by which these gases move into and out of the cell: Diffusion
• Osmosis: The movement of water molecules from an area of their high concentration to an area of their low concentration
• Turgid: When water enters a plant cell and pushes on the cell wall causing the cell to swell
• Plasmolysed: When water leaves a plant cell, the cell contents shrink and the cell membrane pulls away from the cell wall
• Partially Permeable: A membrane that allows some substances to pass through and others cannot.
• Cell A: Cell is flaccid and plasmolysed. Water has left the cell by osmosis across a partially permeable membrane. Water potential inside the cell is higher than the surrounding solution.
• Cell B: Cell is turgid. Water has entered the cell by osmosis across a partially permeable membrane. Water potential inside the cell is lower than the surrounding solution.
• Red blood cells shrink and shrivel when placed in a concentrated salt solution because water leaves the cell by osmosis across a semipermeable membrane. There is a higher water potential inside the cell.
• Red blood cells burst when placed in pure water because water enters the cell by osmosis across a semi-permeable membrane. There is a higher water potential outside the cell. Lack of a cell wall means the cell bursts.
• Syrup (concentrated sugar solution) was produced after two hours because water has moved from an area of higher water potential inside the fruit to an area of lower water potential surrounding the solution by osmosis across a semi-permeable membrane; the sugar has dissolved in the water, producing a syrup.
• Tube A (20% sucrose solution): Tube shrinks because there is a lower water potential outside in the surrounding solution; therefore, water has left by osmosis across a semipermeable membrane.
• Tube B (distilled water): Tube swells up because there is a higher water potential outside in the surrounding solution; therefore, water has entered by osmosis across a semipermeable membrane.

Photosynthesis

• During photosynthesis, light energy is absorbed by chlorophyll, a substance found in the chloroplasts. This energy is then used to convert carbon dioxide from the air and water from the soil into a simple sugar called glucose. Oxygen is also produced and released as a gas.
• Word equation:
  • carbon dioxide + water → glucose + oxygen
• Symbol equation:
  • 6CO2 + 6H2O C6H{12}O6 + 6O2
• If the lamp is closer to the pondweed more oxygen bubbles will be produced. This is because increasing the light intensity increases the rate of photosynthesis meaning more oxygen is released.
• Dependent variable: Number of oxygen bubbles given off
• Independent variable: Distance of lamp from pondweed
• Control variables: Length, species of pondweed, volume of water, temperature, power of bulb.
• The 3 main limiting factors that affect the rate of photosynthesis in a plant:
  • Light
  • Carbon dioxide
  • Temperature
• Wheat field first thing in the morning: Low temperature. Photosynthesis involves enzymes. At low temperatures, enzymes and substrates have low kinetic energy.
• Plants growing on a woodland floor in winter: Low temperature. Photosynthesis involves enzymes. At low temperatures, enzymes and substrates have low kinetic energy.
• Plants growing on a woodland floor in the summer: Reduced light reaching the woodland floor due to blocking by overhead leaves. Light is needed for photosynthesis.

Respiration

• Word equation: oxygen + glucose → carbon dioxide + water
• Symbol equation: 6O2 + C6H{12}O6 → 6CO2 + 6H2O
• Respiration occurs inside a cell in the mitochondria.
• The energy released in respiration is used for:
  • Contraction of muscles
  • Active transport of substances
  • Building up large molecules from small molecules
  • Maintenance of internal body temperature
• Response to exercise:
  • Increased breathing rate
  • Increased heart rate
  • Blood is directed to muscles away from the digestive system
• Word equation for anaerobic respiration: glucose → lactic acid
• Steps leading up to an oxygen debt:
  • Insufficient oxygen is delivered to muscles
  • Glucose → lactic acid via anaerobic respiration
  • Lactic acid needs breaking down which requires extra oxygen
• Word equation for the anaerobic respiration of yeast: glucose → carbon dioxide + ethanol

Gas Exchange (Humans)

• Ventilation is the movement of air into and out of the lungs.
• Breathing in (inhalation):
  • External intercostal muscles contract; ribs move up and out.
  • Diaphragm contracts and flattens.
  • Volume in the thorax increases.
  • Pressure decreases.
• Breathing out (exhalation):
  • External intercostal muscles relax; ribs move down and in.
  • Diaphragm relaxes and is dome-shaped.
  • Volume in the thorax decreases.
  • Pressure increases.
• Adaptations of alveoli for gas exchange:
  • Large surface area
  • Lots of blood capillaries
  • Thin walls provide a short diffusion distance
  • Moist which allows gases to dissolve
• Effect of carbon monoxide on the body: Combines irreversibly with haemoglobin in red blood cells; less oxygen transported.
• Effect of tar on the body:
  • Tar is a carcinogen and may cause lung cancer.
  • Tar paralyses cilia meaning less mucus laden with bacteria is removed.
• Emphysema: Disease caused by smoke damaging the alveolar walls; reduced surface area for gas exchange.
• Nicotine: A drug that makes blood more viscous/thicker leading to increased blood pressure.

Transport (Plants)

• Transpiration is the loss of water vapour from a leaf via stomata.
• The role of the xylem is to transports water and mineral ions from roots upwards to form a continuous column. It is dead tissue which join end to end and lignin strengthens the walls.
• The role of the phloem is to transport sucrose from source to sink both upwards and downwards. It consists of sieve tube elements and companion cells contain lots of mitochondria which release energy needed for active transport.

Transport (Humans)

• Four components of blood:
  • Plasma
  • White blood cells
  • Red blood cells
  • Platelets
• The role of plasma is to transport carbon dioxide, urea, and hormones.
• Adaptations of red blood cells:
  • Biconcave disc shape increases surface area to volume ratio.
  • No nucleus means more oxygen can be transported.
  • Haemoglobin binds to oxygen.
• How the body prevents pathogen entry:
  • Skin acts as a barrier.
  • Hydrochloric acid in stomach kills pathogens.
  • Eyelashes and nose hairs prevent entry.
• The role of platelets is to clot blood at the site of a wound. Soluble fibrinogen is converted into insoluble fibrin.
• How white blood cells attack invading pathogens:
  • Phagocytes engulf pathogens.
  • Lymphocytes secrete antibodies and antitoxins.
• How lymphocytes destroy pathogens: Lymphocytes recognise antigens on pathogens and secrete antibodies which kill pathogens. Antibodies stick pathogens together, and so are more easily recognised by phagocytes.

Heart and Lungs

• a) Heart
• b) Lungs
• The left side of the heart contains oxygenated blood.
• The left atrium receives blood from the lungs.
• The right atrium receives blood from the rest of the body.
• The atria pump blood into the ventricles.
• The role of valves is to prevent backflow of blood.
• The ventricles have thicker walls than the atria because they pump blood further at a higher pressure.
• The left ventricle has thicker walls than the right ventricle because it pump blood further at a higher pressure.
• A double circulatory system means blood passes into the heart twice for every once it passes around the body.

Blood Vessels

• Oxygenated blood is blood carrying oxygen.
• Arteries carry blood away from the heart.
• Veins carry blood towards the heart.
• Arteries have strong walls to withstand the high pressure of blood oxygenated blood a.
• Arteries have elastic walls To withstandhigh blood pressure.
• The function of capillaries is to reach all cells in the body and provide short diffusion distance for respiration.
• The role of the coronary artery is to deliver oxygen to respiring cells and supplies the heart with oxygen needed in respiration.

Blood Flow Through The Heart

• Oxygenated blood from the lungs enters the left atrium from the pulmonary vein. The atrium contracts forcing blood into the left ventricle. This contracts forcing blood into the aorta. Oxygenated blood is delivered around our body to respiring cells. The blood becomes deoxygenated and returns to the right atrium of the heart via the vena cava. The right atrium contracts forcing blood into the right ventricle. The right ventricle contracts forcing blood into the pulmonary artery. Deoxygenated blood flows to the lungs for oxygenation. The pulmonary artery is unusual because the blood flowing through it is deoxygenated. The pulmonary vein is unusual because the blood flowing through it is oxygenated. Arteries carry blood away from the heart, whilst veins carry blood towards the heart. Valves in the heart help prevent the backflow of blood.
• Diets high in saturated fat lead to fat deposits in the wall of the coronary artery. This reduces oxygen flow to heart muscle cells. Less aerobic respiration takes place, more anaerobic respiration occurs. Lactic acid is made which lowers the pH. Enzymes denature causing a heart attack.

Coordination and Response (Plants)

• A plant’s response to a directional stimulus is called Tropism.
• Light:
  • Name of response: Phototropism
  • Response of shoots: Positive
  • Response of roots: Negative
• Gravity:
  • Name of response: Geotropism
  • Response of shoots: Negative
  • Response of roots: Positive
• Water:
  • Name of response: Hydrotropism
  • Response of shoots: Negative
  • Response of roots: Positive
• Auxin concentrates on the side furthest from the light causing cell elongation and stem bends towards the light
• Plant receives more light so more photosynthesis takes place, more glucose made.

Coordination and Response (Humans)

The Nervous System:

• Ears: Sensitive to sound and kinetic energy
• Eyes: Sensitive to light and energy
• Nose and Tongue: Sensitive to chemical energy
• Skin: Sensitive to kinetic and heat energy
• Your nervous system carries fast electrical impulses. Changes in the environment are picked up by your receptors and impulses travel along your neurons to your CNS.
• Stimulus → receptor → sensory neuron → CNS → motor neuron → effector → response

Synapse and Reflex Arc

• In a reflex arc, the electrical impulses bypasses the conscious areas of your brain. The time between the stimulus and the response is as short as possible. Only sensory, relay, and motor neurons are involved.
• Stepping on a sharp pin: The sharp pin is the stimulus. Receptors in the skin detect the stimulus. An electrical impulse passes along the sensory neuron to the relay neuron to the motor neuron. The effector is a muscle which responds by contracting.
• Reflex actions are faster and involuntary and involve the relay neuron.

The Eye

• Controls size of pupil through contractions and relaxation of circular and radial muscles; refracts light, focuses light onto the retina, allows light to enter the eye, contains photoreceptors which are sensitive to light, carries electrical impulses to the brain, stops light refracting inside the eye, tough protective outer layer
• Protects the eye? Sclera
• Contains cells sensitive to light? Retina
• Controls the amount of light entering the eye? Iris
• Refracts light? Lens and cornea
• Connects the eye to the brain? Optic nerve
• Holds the lens in position? Suspensory ligaments and ciliary muscles
• A: Iris
• B: Pupil
• C: Sclera
• Diagram 1; pupil dilates, circular muscles relax, radial muscles contract

Homeostasis (Thermoregulation)

• Homeostasis is the maintenance of a steady internal environment. Thermoregulation, an example of homeostasis, is all about controlling body temperature. It is important that we don’t get too hot as the enzymes in our bodies start to denature. If we are too cold, chemical reactions inside our cells occur too slowly. When we are too hot, vasodilation occurs. This is when arterioles supplying our skin dilate, meaning more blood flows close to the skin and more heat can be radiated. The hairs on our skin lay flat meaning that less insulating air is kept close to the skin. Sweating occurs which helps to cool the body when it evaporates. When we are too cold, vasoconstriction occurs. Arterioles supplying our skin constrict, so less blood flows close to the skin and less heat is lost to the surroundings through radiation. Our hairs on our skin stand on end meaning that more insulating air is kept close to the skin. Shivering takes place which releases heat when our muscles contract.

Reproduction and Inheritance

Reproduction in Humans:

• The female gametes are the egg cells. These are released from the ovary once every 28 days. They are moved down the fallopian tube by cilia (hairs), and this is where fertilisation takes place if sperm cells are present. The uterus is where a fertilised egg can grow into a foetus. It has strong muscular walls and a soft lining. The cervix holds the baby in place during pregnancy. The cervix opens into the vagina, which is where the penis inserts during sexual intercourse.
• The role of the:
  • vagina: A muscular tube where the penis inserts during sexual intercourse.
  • cervix: Holds the foetus in place.
  • uterus: Where foetus grows during pregnancy.
  • oviduct/fallopian tube: Site of fertilisation.
  • ovary: Produces egg cells and oestrogen.
• The male gametes are called sperm cells. These are made in the testes, which are held outside the body in the scrotum. This cools the sperm to the optimum temperature. Sperm cells travel up the sperm duct where fluids are added from the sex glands. This mixture is called semen. Semen flows out of the penis through a tube called the urethra.
• The role of the:
  • penis: Deposits semen in the vagina during sexual intercourse.
  • urethra: Carries urine and semen out of the body
  • sperm duct: Sperm passes from testes to urethra along here
  • testes: Produces sperm and testosterone
• What is the name of the male sex cell? sperm
• What is the name of the female sex cell? egg
• What word is used to describe the fusion of a sperm and egg cell? fertilisation
• Sperm and egg fuse at fertilisation to produce a zygote, cell division by mitosis to form 2 cells, 4 cells, 8 cells, 16 cells.
• Two substances that pass from the mother to the baby: oxygen, glucose
• What passes from the baby to the mother? urea, carbon dioxide
• Where are the sperm cells made? Testes
• Males:
  • Voice deepens
  • Sperm production
  • Pubic hair
• Females:
  • Breast development
  • Menstruation
  • Pubic hair
• Oestrogen repairs uterus lining and secondary sexual characteristics
• Progesterone maintains uterus lining
• Oestrogen is made in the ovaries and placenta
• Progesterone is made in the Corpus Luteum

Reproduction in Flowering Plants

• Fertilization: Joining of pollen and ova
• Pollination: Transfer of pollen from anther to stigma
• Pollen from the anther lands on the stigma. A pollen tube grows down the style into the ovary. The male gamete (pollen) fuses with the female gamete (egg). The ovule becomes the seed, the ovule walls becomes the seed coat, the ovary becomes the fruit.
• Wind Pollinated:
  • Have exposed stamens
  • Feathery stigmas
  • Small petals
  • Small lightweight pollen grains
• Insect Pollinated:
  • Have large colourful petals
  • Scent
  • Nectary

Inheritance

• DNA is a large and complex polymer, which is made up of two strands forming a double helix.
• Chromosomes are contained inside the cell's nucleus. These are made from long strands of DNA.
• A haploid number of chromosomes is one copy of each chromosome. In humans, this number is 23.
• A diploid number of chromosomes is two copies of each chromosome. In humans, this number is 46.
• A gene is a small section of DNA that codes for a particular sequence of amino acids that make a specific protein.
• An organism's genome is one copy of all of their DNA.
• Dominant alleles are expressed even if only one allele is present (e.g., Bb). Recessive alleles require both alleles to be present in order for the phenotype to be expressed (e.g., bb).
• Polygenic inheritance is when a phenotype is controlled by more than one gene.
• Most phenotypic features in humans are the result of polygenic inheritance.
• Gene: Section of DNA which codes for a protein
• Allele: A form of a gene
• Phenotype: Physical appearance of a gene
• Genotype: The alleles an organism has
• Homozygous: 2 copies of the same allele
• Heterozygous: 2 different alleles
• Dominant: Allele expressed even if only 1 is present
• Recessive: Allele only expressed if dominant allele is absent
• Mutation: Spontaneous, random change in DNA
• Two different forms of the same genes are called alleles
• If someone has two copies of the same allele they are homozygous
• If someone has two different copies of an allele they are heterozygous
• Your phenotype is the physical expression of your genes
• Your genotype is the combination of alleles you have
• Recessive alleles need two copies of the same allele to show that phenotype
• Dominant alleles only need one copy to be present to show that phenotype
• Dominant alleles are always written as capital letters.
• Recessive alleles are always written as lower case letters.

Punnett Squares

• Cystic Fibrosis: all offspring are carriers. (Ca)
  100% carrier

*Broad Leaf
*50% broad
*50% narrow

• Huntington’s Disease: 75% chance disease, 25% healthy. (Hh)
  Sickle Cell Anaemia: all offspring healthy. Aa (Aa)
  Marfan Syndrome: Person A; heterozygous for MS. Most are heterozygous. Dd Dd
  Probability: 0.5 x 0.5 x 0.5 = 0.5?

Mitosis and Meiosis

• A cell that has two sets of chromosomes. In humans, almost all cells apart from the sperm and the egg cells are diploid
• Having one set of chromosomes i.e. gametes
• Sex cell (sperm or egg cell) produced in the male or the female reproductive organs by meiosis
• A section of DNA that codes for a specific protein
• The structure that DNA is packaged into. Humans have 23 pairs – 1 pair from each parent.
• The region of the cell where DNA is found
• The molecule we inherit from our parents. It is packaged into chromosomes and found in the nucleus.
• Different form of the same gene. E.g. the gene for eye colour has a number of alleles – blue, green, brown, hazel.
• Reproduction that does not involve the fusion of gametes. The offspring are clones of the parents.
• Reproduction that involves the fusion of 2 gametes to create a genetically unique individual. It is common in animals and plants.
• The cell division of normal body cells that produces 2 identical cells.
• The cell division that takes place in the reproductive organs to produce gametes. It produces cells with just 23 chromosomes (one of each pair).

Natural Selection

• Random mutation has lead to variation in moth wings and so better camouflaged black moths are more likely to survive and reproduce; therefore, more favourable alee will be passed on to offspring.
• Random mutation has lead to variation in giraffe spears and so the ones that now have long necks are more capable of reaching food; therefore, they are more likely to survive and reproduce and the favourable allele will be passed on to offspring
• Why does a camel have:
  • long eyelashes: Prevents sand entering eye
  • big feet: Decreases pressure so less sinking into sand
  • thin fur: Less chance of overheating
  • a hump: Stores fat
• Spine instead of leaves, prevents transpiration; stem stores water and shallow extensive roots help absorption
• Give 4 ways in which a polar bear is adapted to live in cold, snowy conditions
  • White fur camouflaged whilst hunting pray
  • Thick fat layer provides insulation
  • Large paws reduce pressure and stops sinking into snow
  • Small ears reduce surface area to volume ratio so less heat loss

Ecology and the Environment

• Producer: Plants which photosynthesis and produce glucose
• Herbivore: Animals which feed on plants animals
• Consumer: Animals which feed on plants animals
• Predator: Animals which hunt kill eat other animals
• Prey: An animal which is killed and eaten by other animals
• Name the 3 producers in the food web:
  Wheat
  Grass
  Carrot
  Name 2 organisms which are in competition for their prey
  Owls
  Birds
  What would happen if mice died: 1)Wheat would increase; 2)owls would decrease; 3)Grasshoppers would decrease
• All the energy in the food web come from the sun
• Light and Mineral ions

Carbon and Abiotic

• Abiotic: non living factors (temp, pH)
• Biotic: Living factors (disease, predation, parasitism)

The Effects of Leached Sewage

• Eutrophication occurs. Nitrates enter the water causing algal bloom. Plants die due to the competition for light. Decomposers feed on the algae and increase in number. Decomposers use up oxygen in the water during respiration. The water is anoxic and fish and other aquatic organisms die.
• Global warming leads to polar ice caps melting, sea levels rise, loss of low lying land. Loss of habitat leads to the loss of biodiversity. Bird migration patterns change and extreme weather occurs.
• Carbondioxide, methane,