A-Level

In Parkinson’s disease neurons in the brain die. All these neurons secrete  dopamine neurotransmitter, which causes difficulty in movement and limb shaking.   In depression neurons in the brain that secrete serotonin neurotransmitter stop working properly and...

Drugs that affect synapses can drastically alter the functioning of the brain;   MDMA:   Active ingredient in ecstasy. This binds to protein pumps on the pre-synaptic membrane of nerves that secrete serotonin. The pumps would normally take serotonin up after it...

Continuous variation: there is a wide range of phenotypes (e.g. height)   Discontinuous variation: phenotypes fall into discrete categories (e.g. blood type)   Discontinuous variation tends to be coded for by one gene with a few different alleles. However,...

Brain development is a combination of nature and nurture.

Pavlov’s Dogs   Pavlov had observed that an unconditioned stimulus causes an unconditioned response, i.e. food causes salivation. This is not learned and is, therefore, unconditioned. What Pavlov discovered was that if a neutral stimulus, such as a bell is rung just...

How to process stimuli correctly must be learned. The cortex is split into column of cells. When we are born, the columns overlap and are tangled. As we learn to process stimuli, the cells organise themselves into discrete columns, which no longer overlap. There is a...

The Muller-Lyer illusion; Lines A and B are the same length, yet look different – why? The answer is that you have learned to process this kind of stimuli in a certain way. We live in a “carpentered world” of straight lines and we interpret line B as a corner...

Association (classical conditioning):   US ® UR         (Food ® Salivation) Over time, if a neutral stimulus (CR) is played with the US, it becomes associated  with the US and begins to elicit the same response. Eventually, the animal learns CS ® CR          (Bell ®...

Hindbrain   Brainstem – Uppermost part of the spine, where the spine joins the brain.   Medulla - controls vital ‘housekeeping’ functions, such as heartbeat, blood pressure and peristalsis. Cerebellum - controls muscle co-ordination & learns motor programmes...

Visual  transduction  is  the  process  by  which  light  initiates  a  nerve  impulse. The structure of a rod cell is: The detection of light is  carried out on the membrane disks in the outer segment. These disks contain thousands of molecules of rhodopsin, the...

Homeostasis is the maintenance of the internal environment. Nerve reflexes give immediate responses Hormone responses give responses over weeks – months Hormones are released from glands, which release hormone into the blood. The hormone is carried all over the body....

A  synapse  is  the  junction  between  two  nerves.  It  is  also  a  verb,  i.e.  one nerve synapses with another (meaning, passes a message to another). The neurotransmitter on your syllabus is Ach, but over 2000 other transmitters have been discovered. The wave of...

Sequence of events in an action potential;   Nerve is at resting membrane potential (-70mV) A stimulus depolarises the nerve to threshold (-50mV) Voltage-gated Na+ Channels open Sodium floods  into  the  cell  and  the  membrane  potential  depolarises to +30mV...

Why should we allow use of drugs;   Gives people a chance to be as good as their potential allows Removes “unfair” genetic advantages Controlled use of drugs is less risky People should have the right of choice Legalising drugs makes their distribution...

Sensory nerve:           carries electrical message from receptor to spine   Motor nerve:              carries electrical message from spine to effector.   Relay nerve:               connects sensory and motor nerves. Also relays message to the brain....

High light intensity Circular muscles: contracted Radial muscles: relaxed Pupil diameter: small Low light intensity Circular muscles: relaxed Radial muscles: contracted Pupil diameter: large  

     A moderate level of exercise improves health & well-being. However, over-training can result in  the opposite effect. This is the phenomenon known as “burn-out”     Positive effects of exercise include;   Increased BMR Decreased blood...

Key-hole surgery is a technique which allows doctors to conduct surgery with the minimum possible damage to the patient. The surgeon makes a small incision (a “key-hole”) and uses a fibre-optic camera to view the damaged area. If required, the surgeon can make a...

See 4.6.11 for mechanisms of thermoregulation. The thermoregulatory process (and most homeostatic systems) are controlled by negative feedback processes. If a system changes, it is detected, a homeostatic response is activated, which aims to return the system to its...

A spirometer is used to plot breathing patterns   Vital Capacity: The maximum amount of air a person can exhale   after inhaling the maximum possible volume of air Tidal Volume: The volume of air inhaled & exhaled in one breath Basal Metabolic Rate: The rate...

Sprinters need lots of fast twitch muscle, joggers need slow twitch. Therefore, the muscle type of a cheetah or a gazelle will be predominantly fast twitch, whereas the muscle of a camel or an elephant will be predominantly slow twitch. Muscle type in humans is...

  Adenosine TriPhosphate (ATP) is made from three components;   Ribose (the same sugar that forms the basis of DNA). A base (a group consisting of linked rings of carbon and nitrogen atoms); in this case the base is adenine. Up to 3 phosphate These...

  In anaerobic respiration lactate is taken via the blood to the liver, where it is broken down into pyruvate using oxygen and NADH.

Muscles are made from muscle fibres arranged into bundles. Each fibre is made from bundles of myofibrils, which are extremely long, cylindrical muscle cells. The functional unit of contraction is the sarcomere. Muscle cells contain many sarcomeres arranged in...

We have evolved a very effective immune system, consisting of barriers, non-speficif  defence mechanisms and specific ones. If we’re so good at fighting infections, why do we  still get ill?   Answer: pathogens are evolving as well. So how has TB evolved to beat...

Antibiotics work by targeting prokaryotic features not found in eukaryotic cells, e.g. penicillin targets the cell wall and breaks it down. Penicillin can be taken in large doses by humans because it has no effect on our cells (we have no cell walls).  ...

The effectiveness of antibiotics can be measured using a disc diffusion technique.   A bacterial lawn is grown on an agar plate (either by spreading the bacteria over the plate, or by using a pour plate).   A disc of blotting paper is soaked in antibiotic of...

Bacteria are becoming resistant to antibiotics. Bacteria develop resistance  through mutation. A bacteria can mutate and develop resistance by;   Having an enzyme that breaks the antibiotic down   Having a protein which pumps antibiotic out of the cell...

The evolutionary arms race between bacteria and drug developers is, at the moment, tipped against humans. There are over 100 different types of antibiotic and in the 40years since their development 4 species of  bacterium have developed resistance against  all  of   ...

Cartilage: a tissue made from collagen, which protects bone ends A muscle: an organ that produces movement by contraction A joint: the junction between two bones A tendon: joins muscle to bone A ligament: joins bone to bone to stabilise a joint Muscles work in pairs....

Homeostasis is the maintenance of the body’s internal environment. This is carefully controlled by a series of systems, which aim to keep conditions at a stable controlled level. Body Tempereature Body temperature is carefully regulated to maintain a steady 37.5˚C,...

Barrier Mechanisms include; Skin, Stomach Acid, Normal Flora, Epithelial cells. Skin adaptions for defence The skin is made from 2 layers Outer epidermis layer Inner dermis layer The epidermis provides a physical barrier to invading pathogens. There are 2 layers in...

Both T and B Cells differentiate into Memory Cells, which remain in our lymph nodes and wait until we are re-exposed to the same pathogen.   When the Memory B cell is activated by the old antigen it makes large quantities on  antibody quickly and kills the...

Negative feedback systems aim to keep something (e.g. blood [glucose] or body temperature) at a constant level.   Negative feedback works as follows;   Signal causes action   Action has effect   Effect removes original   E.g.   High...

Pathogens have proteins on their surface that our immune system has learned to recognise as foreign. These proteins are called antigens. T cells, B cells & Macrophages all have the ability to recognise an antigen and once this has happened, they will trigger an...

There are two different types of Immune Response; A Cell-mediated Immune Response B             Antibody-mediated Immune Response.   NB:          ISOLATED VIRUSES DO  NOT PRESENT ANTIGENS AND THEREFORE DO   NOT TRIGGER EITHER THE CELL- OR ANTIBODY-MEDIATED IMMUNE...

A typical prokaryot Ribosomes. Same function as eukaryotic cells (protein synthesis), but are smaller (70s rather than 80s).   Nuclear Zone. The region of the cytoplasm that contains DNA. There is no nuclear membrane. DNA. Always circular, and not in chromosome...

COURSE OF  INFECTION FOR TUBERCULOSIS : Tuberculosis (TB) is caused by the Mycobacterium tubercolusis bacterium.   Mycobacterium tuberculosis is inhaled into the lungs in droplets of water & mucus from another person’s lung (droplet infection)   TB...

Inflammation: damaged white blood cells and mast cells release histamine at the site of infection. Histamine causes local arterioles to vasodilate, increasing the blood supply to the area. It also causes holes to open between endothelial cells in capillary walls. This...

The identity of a dead person can be ascertained by;   Identity papers – Fingerprints Dental records Genetic Fingerprint   Fingerprints: The skin on fingers, toes etc is ridged into specific patterns (arches, tented arches, whorls & loops). Sweat and...

The idea that as each organism or group of organisms feeds on a body, it changes the body. This change in turn makes the body attractive to another group of organisms, which changes the body for the next group, and so on until the body has been reduced to a skeleton....

Time of death can be measured using the following factors; Body temperature Extent of rigor mortis Level of decomposition Forensic entomology Body Temperature A body cools following an S-shaped (sigmoid) curve. The initial plateau at 37˚C lasts 30 – 60 min, then the...

Isolation is important for evolution because it decreases the size of the gene pool. This stops new alleles coming in from breeding with original alleles and speeds the accumulation of new mutations (which is what leads to speciation). The different types of isolation:

Evolution is a theory, not a fact. Many people believe that species were created (creationism). Other people believe in evolution, but by mechanisms other than Natural Selection. You should respect the opinions of other people, even if you do not necessarily agree...

Primary succession is the first stage of the ecological succession of plant life from abiotic land with no soil to fully support plant ecosystems (e.g., a forest). In primary succession, pioneer plants like mosses and lichen, start to "normalize" the habitat, creating...

Zoos can play a large role in conserving endangered species by; 1. Conducting research 2. Running captive breeding programmes 3. Reintroducing species into the wild 4. Educating people Research enables scientists to understand the role of a species in an ecosystem. By...

There are no set facts to learn.

There are no set facts to learn.

Evolution: the idea that one species changes into another over time Natural Selection: Darwin’s suggestion for the process by which evolution might occur Evolution by Natural Selection (Darwinian Evolution) 1. There is variation in a species 2. More individuals are...

1798 Malthus publishes paper on population growth. Malthus noticed that the human population was expanding exponentially. He thought that the human population would outgrow its resources and that this would lead to famine and war. Darwin was influenced by this idea,...

NPP = Net Primary Productivity (amount of stored chemical energy the plant has to use for growth. This is directly proportional to biomass) GPP = Gross Primary Productivity (amount of stored chemical energy the plant earns through photosynthesis) R = Respiration...

Energy is lost between trophic levels. Energy is lost in the following ways; in respiration (mostly lost through heat), energy still present in egested food, through movement, through digestion, energy still present in excreted materials etc Of the 100% sunlight...

There are three steps in the Calvin Cycle; 1. Carboxylation: RuBP fixes CO2to form GP. This reaction is catalysed by the enzyme Rubisco 2. Reduction: In a series of reactions GP reacts with ATP and NADPH reduced GP to form GALP (by reducing GP the NAHPH itself is...

Thylakoid membrane = location of photosystems & electron transport chain Stroma = site of Calvin Cycle & photolysis of water Grana provide large surface area for absorbtion of light

Dihybrid Crosses are for crosses involving two different genes (2 loci). A = Purple stem, a = Green Stem, D = Big Leaves, d = little leaves F1 Phenotype: 9 : 3 : 3 : 1 A_B_ : A_bb : aaB_ : aabb Purple & Big : Purple & Little : Green & Big : Green &...

Biotic Factor: A living variable within the ecosystem, which affects the survival of organisms. Examples include predation, competition, and pollution from excreted waste. Abiotic Factor: A non-living variable within the ecosystem, which affects the survival of...

Figure 5.33 – in the light dependant reactions of photosynthesis, the energy from the sun excites chlorophyll molecules. High energy electrons leave the chlorophyll and pass along a series of carrier proteins in the electron transport chain. The ionised chlorophyll...

Individuals in the same species look different (have different phenotypes). This is called variation. Variation is caused by; The genotype of the individual (i.e. which alleles they have). The environment. Genetic diversity describes the range of different genotypes...

Possible Future Treatments   Gene therapy: The genotype (therefore the phenotype of target cells) is altered: Normal alleles of the gene are inserted into the target cells using a genetically modified virus or using liposomes (spherical phospholipid bilayers) The...

A particular species can be identified using the features (the phenotype) which are characteristic to only that species. Species with similar phenotypes are likely to be related to each other. A key of characteristics is used to identify the species. (see p10 – 11)...

What goes wrong with DNA? A mistake in translation can produce mRNA with one or more incorrect codons Error in cystic fibrosis sufferers is in the DNA as the problems are in every epithelial cell Mistakes arise when DNA copies itself curing the process of DNA...

Cystic Fibrosis Inheritance   Genes and chromosome pairs: Gene; a length of DNA that codes for a protein Every cell (except sex cells) contain two copies of each gene, one from each parent Both copies have the same locus on each of the paired chromosomes 23 pairs...

Treatment of Cystic Fibrosis   Medication Diet Digestive Enzyme supplements Physiotherapy Heart and lung transplant ·         Bronchodilators ·         Antibiotics ·         DNAease enzymes ·         Steroids ·         High energy foods ·         Salt supplements...

CFTR Protein Cystic fibrosis is caused by a mutation in the DNA that carries the instructions for making the CFTR protein   Structure of DNA: James Watson and Francis Crick proposed model for DNA based on X-ray diffraction patterns DNA is found in every cell...

Enzyme Function Globular proteins that act as biological catalysts Speed up chemical reactions that would normally be slow at cell temperature Precise 3-D shape includes a depression surface; active site Amino acids involved on active site whilst other remain 3-D...

Reproductive System Females have reduced chance of pregnancy; mucus plug develops in the cervix Men usually lack the sperm duct on both sides which means sperm cannot leave the testes If the sperm duct is present, it is usually blocked by sticky mucus

Digestive System People with CF have a high basal metabolic rate Pancreatic duct becomes blocked with sticky mucus, stop the release of digestive enzymes Lower concentration of enzymes in the small intestine reduces the rate of digestion Food is not fully digested so...

Water Regulation; unaffected lungs Cells that line the airways produce mucus Water in the mucus is continuously regulated to maintain a constant viscosity Must be runny enough to be moved by beating cilia However it cannot be so runny that the fluid floods the airway...

Transport of Substances through Cell Membrane       Type of molecule Examples Through which part of the membrane Active or passive With or against the concentration gradient Diffusion Small, uncharged molecules Carbon dioxide and oxygen Phospholipid bilayer...

Cell Membrane Structure   Phospholipid Bilayer: CF: caused by a faulty transport protein in the surface membranes of epithelial cells Basic structure of the bilayer is two layers of phospholipid   Phospholipid Molecule: Only has two fatty acids; negatively...

DNA: DNA is a type of nucleic acid called deoxyribonucleic acid. It is a long chain molecule made up of nucleotides. One nucleotide is made up of: A 5 carbon sugar A phosphate group An organic base Nucleotides link together by condensation reactions between the sugar...

Genetic Screening: Genetic screening is used to: Identify carriers: heterozygotes with normal phenotypes. This can be followed up with counselling to help potential parents make a decision. Embryo testing: a sample of cells from a developing foetus can be analysed....

Protein Structure General Structure All composed of the same basic unites – amino acids 20 different amino acids Plants can make all these amino acids, animals can only make some Animals obtain the other amino acids through diet; essential amino acids   Amine...

Movement across the plasma membrane: Osmosis: the movement of water molecules from high concentration to low concentration through a partially permeable membrane. Diffusion: the movement of molecules or ions from an area of their high concentration to an area of their...

Proteins: Structure of an amino acid: The amino acid monomers join together in a condensation reaction to form peptide bonds. The polymer formed is called a polypeptide. How do they form? Primary structure: the sequence of amino acids in the polypeptide chain. Amino...

Enzymes: Are globular proteins which act as catalysts. They speed up chemical reactions by lowering the activation energy, and remain unchanged at the end of the reaction. They provide an alternate reaction pathway, which requires less energy to start. Part of the...

Heart and Circulation: In small unicellular organisms, substances move around slowly by diffusion. Diffusion is too slow to move substances round the larger bodies of multicellular organisms. Thus has a circulatory system: substances are carried in blood pumped by a...

Cell Membrane: Cell membrane is made up of a phospholipid bilayer. The phosphate head of the phospholipid is a polar molecule and attracts water – it is hydrophilic. The fatty acid tails are non-polar and hydrophobic. In the cell membrane, the hydrophobic tails face...

Carbohydrates: They have a general formula: Cx(H2O)n Saccharides are made from sugar molecules that are made from combinations of the elements carbon, hydrogen, and oxygen only. They are used for: Fuels for respiration (glucose). Energy storage molecules (starch and...

Lipids: Triglycerides are either fats or oils. They are made from the elements carbon, hydrogen, and oxygen only. They are insoluble in water. Triglycerides are used for: Long term energy storage molecules Insulation Protection (pericardium) Buoyancy Synthesis of...

Water: Water molecules are non-linear and polar molecules because the H and O atoms are different in size and electronegativity. They form hydrogen bonds with other water molecules. Some properties include…     Property Explanation Excellent solvent...