GCSE Biology Revision Notes PDF

# LearnSmart.Academy **Local, trusted tuition** ## GCSE Biology Revision ### Chapter 1: Cell Biology #### Organisation | Level | Example | |---|---| | Organisms | Human | | Organ Systems | Cardiovascular System | | Organs | Heart | | Tissues | Blood Vessel Cells | | Cells | Plant cell | #### C...

# LearnSmart.Academy **Local, trusted tuition** ## GCSE Biology Revision ### Chapter 1: Cell Biology #### Organisation | Level | Example | |---|---| | Organisms | Human | | Organ Systems | Cardiovascular System | | Organs | Heart | | Tissues | Blood Vessel Cells | | Cells | Plant cell | #### Cell Structure - **Eukaryotic cells** have a cell membrane, cytoplasm and nucleus. - **Prokaryotic cells** have cytoplasm, membrane and cell wall; genetic material not in a nucleus. - bacteria and some algae #### Animal and Plant Cells - **Animal cells** have cell membrane, cytoplasm, nucleus, ribosomes and mitochondria. - **Plant cells** have cell wall, vacuole, cell sap, chloroplast, cell membrane, cytoplasm, nucleus, ribosomes and mitochondria. #### Cell Differentiation - Animal cells start to differentiate early in their life. - Plant cells are able to differentiate throughout its life. - Once a cell has differentiated, it can only produce one type of tissue. (stem cell --> specialised cell) #### Stem Cells - In animals, stem cells are found in the bone marrow, which can be used to treat diabetes or paralysis. - In plants, stem cells are found in the meristem tissue at the end of growing roots and shoots. #### Examples of Specialised Cells | Type | Examples | Function | |---|---|---| | Animals | Sperm cells, nerve cells, muscle cells | Perform different functions | | Plants | Root hair cells, xylem cells, phloem cells | Adapt to perform specific functions | #### Microscopy The resolution of a microscope is dependent on the size of the wavelength of light used. | Type of Microscope | Wavelength of Light | Function | |---|---|---| | Electrons | Tiny Wavelength | View sub-cellular structures | | X-rays | Small Wavelength | View cell structures | | Visible Light | Large Wavelength | View tissues | **Magnification = size of image / size of object** #### Cell Division - **Haploid cells** have half the normal number of chromosomes: 23 chromosomes. - **Diploid cells** have the normal number of chromosomes: 23 pairs of chromosomes or 46 chromosomes. #### Before a Cell Divides - It grows. - It increases the number of ribosomes and mitochondria. - The DNA replicates. - The cytoplasm and cell membrane divide. #### Mitosis (normal cells) - Starts with a diploid cell. - DNA replicates. - Ends with two diploid cells. #### Meiosis (sex cells) - Starts with diploid cell. - DNA replicates. - Splits into four haploid cells. - Ends with four haploid cells. #### Transport in Cells ##### Diffusion - The spreading out of particles from a high concentration to a low concentration. Factors: - Concentration gradient - Temperature - Surface area of membrane Examples: - Gas exchange in lungs - Waste products in kidneys ##### Osmosis - The spreading out of water particles from a high concentration to a low concentration. Factors: - Water concentration gradient - Temperature - Surface area of membrane - Permeability of the surface Examples: - Water absorption in intestines #### Active Transport - The spreading out of particles from a low concentration to a high concentration. Note: This takes energy, so it always occurs in the presence of mitochondria and glucose. Factors: - Concentration gradient - Temperature - Surface area of membrane - How much energy is available Examples: - Water re-absorption in the kidneys #### Chapter 2: Organ Systems #### Digestive System | Part | Function | |---|---| | Mouth | Chewing and breaking down food with saliva | | Oesophagus | Connects mouth to stomach | | Stomach | Churns food and mixes it with digestive juices | | Pancreas | Produces digestive enzymes | | Liver | Produces bile | | Gall Bladder | Stores and concentrates bile | | Intestines | Absorbs nutrients from food | #### Enzymes - Enzymes work at body temperature (around 40°C). - If it's too hot, the enzyme can become denatured. - If it's too cold, the enzyme becomes inactive. #### How Enzymes Work - Enzymes use the "lock and key" method. - Enzymes create a confined area (active site) for the chemical reaction, reducing the activation energy. #### Digestive Enzymes | Enzyme | Produced in | Released in | Referred PH | |---|---|---|---| | Amylase | Salivary glands & pancreas | Mouth & small intestine | Neutral & Alkaline | | Maltase | Small intestine | Small intestine | Alkaline | | Protease | Small intestine | Small intestine | Alkaline | | Pepsin | Stomach | Stomach | Acidic| | Lipase | Pancreas | Small intestine | Alkaline | #### Villi - Villi in the small intestine increase the surface area of nutrient absorption. - Villi hugely increases the length of blood vessels available for absorption. #### Cardiovascular System #### Blood Vessels - **Arteries** carry blood away from the heart at high pressure. - Arteries have thick walls. - **Veins** carry blood towards the heart at lower pressure. - Veins have thinner walls. - Veins contain valves. - **Capillaries** carry blood through tissues, performing gas and nutrient exchange. - Capillaries have thin walls. #### Blood - **Blood** is made up of: - **Red blood cells**: contain haemoglobin for carrying oxygen. - **White blood cells**: part of the immune system. - **Plasma**: fluid part. - **Platelets**: for clotting. #### The Heart - **Pulmonary** refers to to and from lungs. - **Aorta** refers to the main artery. #### Heart Health Issues - **Coronary heart disease**: fat/cholesterol levels. - **Heart attack**: heart cells die and malfunction due to lack of blood supply. - **Valve malfunction**: valves stop working properly. #### Treatments - **Transplant**: body can reject. - Very invasive surgery. - **Mechanical substitution**: can malfunction. - Body can reject. - **Drugs**: e.g. statins for coronary heart disease. - Treat, not fix. #### Causes of Heart Disease - **Defects in the immune system**. - **Hereditary susceptibility**. - **Lifestyle choices**: diet, drink, drugs, radiation, exercise. #### Plant Tissues - **Upper epidermis**: protects plant from weather damage. - **Palisade mesophyll**: specialised for photosynthesis. - **Spongy mesophyll**: provides air spaces for gas exchange. - **Lower epidermis**: contains stomata. - **Stomata**: holes created by guard cells. - **Guard Cells**: control the transfer of water and gases into the leaves. - **Xylem**: transports water and minerals around the plant. - **Phloem**: transports sugars and glucose around the plant. - **Meristem tissue**: found at the end of growing roots and shoots. #### Chapter 3: Infection and Response #### Communicable (Infectious) Disease Communicable diseases are caused by pathogens, which are micro-organisms that change or damage cell function: - **Viruses**: parasites of cells. - **Bacteria**: release toxins. - **Fungi**: contain cells. - **Protists**: contain cells. #### Pathogen | Type | Animal Diseases | Plant Diseases | |---|---|---| | Viral | Measles, HIV | Tobacco Mosaic Virus (TMV) | | Bacterial | Salmonella, Gonorrhoea | Rose Black Spot | | Fungal | | | Protist | Malaria | | #### Human Defence System ##### Non-Specific Doesn't specific to a certain pathogen/infection. - **Skin**: acts as a physical barrier, - **Nose hairs**: trap particles. - **Bronchi and mucus in trachea**: trap particles. - **Stomach acid**: kills bacteria ##### Specific Different depending on a specific pathogen/infection. - **White blood cells**: produce antibodies. - **Antibodies**: produce antitoxins. - **Memory lymphocytes**: retain memory of previously seen pathogens to speed up repeated response. #### Vaccinations - **Weak or dead versions of the pathogen** are injected to stimulate a response and antibody production. - **Booster vaccinations** are needed to for the memory lymphocytes to share the information. #### Treating Disease | Treatment | How it works | Examples | Downsides | |---|---|---|---| | Antibiotics | Antibiotics produce antitoxins | Penicillin | Bacteria are mutating, so can’t be used as much. | | Painkillers | Can be used to reduce fevers and lower pain | Paracetamol, Ibuprofen | Treats the symptoms, not the cause. | #### Drug Development - **Low doses** are given to a small sample of healthy people to test the drug and assess its safety. - **Clinical trials** involve testing of the drug with a placebo, which is a fake drug. - The trials use a double-blind method, where neither the doctors or the patients know who has been given the placebo to avoid psychological bias. - **Larger clinical trials** are carried out to further assess the drug's efficacy and confirm its safety. - **Production** stage involves large scale production of the drug. #### Drugs from Natural Sources - **Digitalis**: is a heart drug derived from foxgloves. - **Aspirin**: is derived from willows. - **Penicillin**: is an antibiotic derived from mould. #### Plant Diseases You can detect if a plant has a disease by: - **Stunted growth**. - **Leaf spots**. - **Decay/rot**. - **Extra growths**. - **Malformation**. - **Discoloration**. - **Pest infestation**. #### Examples of Plant Diseases | Plant Disease | Type | |---|---| | TMV | Viral | | Black spot | Fungal | | Aphids | Insects | | Ion deficiency | Shunted growth | | Magnesium deficiency | Chlorosis | #### Plant Defence | Defence | Type | Examples | |---|---|---| | Cell walls | Physical | | | Waxy cuticles | Physical | Layers of dead cells | | Anti-bacterial | Chemical | | | Poisons | Chemical | | | Thorns | Mechanical | | | Drooping leaves | Mechanical | | | Mimicry | Mechanical | | #### Chapter 4: Bioenergetics - **Bioenergetics** is the process organisms create and use glucose. #### Creating Glucose - **Photosynthesis** is how plants create glucose. - **Plants** contain **chloroplasts**, which are organelles that use light energy to synthesise glucose from carbon dioxide and water. **6CO2 + 6H2O LIGHT C6H12O6 + 6O2** - **Photosynthesis** is an **endothermic reaction**. It takes in heat (light) from the surroundings. #### Rate of Photosynthesis The rate of photosynthesis depends on: - **Temperature**. - **Light intensity**. - **CO2 concentration**. - **Amount of chlorophyll** (contained in the chloroplast). #### Uses of Glucose - **Respiration** for active transport and muscle movement. - **Insoluble starch** for storage in the phloem. - **Fat or oil** for storage. - **Cellulose** that strengthens the cell wall. - To produce **amino acids** for protein synthesis. #### Using Glucose - **Respiration** is how organisms use glucose to release energy. - Both plants and animals respire for active transport and to do so, require **mitochondria**. **C6H12O6 + 6O2 --> 6CO2 + 6H2O** - **Respiration** is an **exothermic reaction**, releasing energy to the surroundings. - Organisms need this energy for chemical reactions, movement and keeping warm. #### Anaerobic Respiration - **Anaerobic respiration** means respiration lacking in oxygen. - **Anaerobic respiration** in muscles produces **lactic acid**. - **Anaerobic respiration** in yeast cells produces **ethanol + CO2**. #### Metabolism & Exercise - **Metabolism** is the body's ability to convert and use glucose. - You can speed up the metabolic rate by exercising. #### When Exercising: - **Heart rate** increases. - **Breathing rate** increases. - **Breath volume** increases. #### After Long Periods of Vigorous Exercise - The body cannot gain enough oxygen, so it respires anaerobically. - The blood picks up **lactic acid** and drops it off at the liver to transform back into glucose. #### Chapter 5: Homeostasis **Homeostasis** is the regulation of internal conditions to keep optimal conditions for cells and enzymes. #### Main Examples of Homeostasis - Maintaining blood glucose concentration. - Control of body temperature. - Control of water levels. #### Control Systems - **Control systems** consist of receptors, coordination centres and effectors. - **Receptors**: detect stimuli. - **Coordination centres**: process information. - **Effectors**: create a response. #### Control Systems | Component | Job | Examples | |---|---|---| | Receptors | To detect stimuli | Sensory neurons | | Coordination centres | To process information | Brain and CNS | | Effectors | To create a response | Motor neurons and glands | #### Human Nervous System - **High level**: stimulus --> receptor --> coordination centre --> effector --> response ##### In More Detail - **Sensory neuron** --> **Relay neuron** --> **CNS** --> **Relay neuron** --> **Motor neuron** - **Reflex relay neuron** ##### Synapses - **Pre-synaptic cells** release **serotonin**. - **Serotonin receptors** on the **post-synaptic cell** receive serotonin. - An **electrical impulse** is triggered. #### Control of Blood Glucose Levels - **Blood glucose concentration is controlled and monitored by the pancreas**. #### If Blood Sugar Level is Too High: - The pancreas produces **insulin**. - Insulin causes glucose to move from blood to cells. - **Excess glucose** in the liver is converted to **glycogen** for storage. #### If Blood Sugar Level is Too Low: - The pancreas ceases **insulin production.** - The pancreas produces **glucagon**. - Glucagon causes glucose to move from cells to blood. #### Diabetes | Type | Description | Cause | Treatment | |---|---|---|---| | 1 | Pancreas fails to produce sufficient insulin. | Hereditary | Insulin injections or transplant. | | 2 | Body cells no longer respond to insulin | Lifestyle choices | Carbohydrate-controlled diet. | #### Control of Body Temperatures - **Body temperature** is monitored by the **thermoregulatory centre** in the brain by measuring blood temperature. #### If Body Temperature is Too High: - **Blood vessels dilate** to promote heat loss. - **Sweat is produced** to cool the body. - **Hair flatters** to allow for heat loss. #### If Body Temperature is Too Low: - **Blood vessels constrict** to minimise heat loss. - **Sweating stops** to prevent further heat loss. - **Hair raises** to trap a layer of warm air, acting as an insulator. - **Skeletal muscles contract** (shiver) to generate heat. #### Maintaining Water Levels - **Water leaves the body** in multiple ways. - Some we control, others we don't. #### Examples of Water Loss - **Lungs** during exhalation. - **Sweat**. - **Wea** (urine). #### Controlling Water Levels - **The kidneys** play a crucial role in controlling water levels. #### Chapter 6: Inheritance, Variation and Evolution #### Important Terms Involved in Reproduction | Term | Meaning | |---|---| | Haploid | Cell with half normal DNA (chromosome number).| | Diploid | Cell with normal DNA (chromosome number). | | Gamete | Haploid sex cell. | | Chromosome | Section of DNA grouped in shell. | | Gene | Small section of DNA within a chromosome | | Allele | Variant form of a gene. | | Dominant | Allele which wins. | | Recessive | Allele which gives in. | | Homozygous | Has two like alleles. | | Heterozygous | Has two different alleles. | | Genotype | Genetic constitution (Bb) | | Phenotype | Observable characteristics. | #### Sexual Reproduction - Joining of male and female gametes. - In animals, the gametes are sperm and egg cells. - In plants, the gametes are pollen and egg cells. #### Advantages of Sexual Reproduction - Produces variation. - Can adapt better to the environment. #### Asexual Reproduction - One parent, no fusion of gametes. - No mixing of genetic material so all offspring are clones. #### Advantages of Asexual Reproduction - Time and energy-efficient. - Faster. - Can produce favourable genes. #### DNA - **DNA** is a polymer made up of two strands forming a double helix. - **DNA** is contained in structures called **chromosomes**. - A **gene** is a small section of DNA on a chromosome. - Each gene codes for a particular sequence of amino acids to make a specific protein. - A **genome** is the entire genetic material of an organism. #### DNA Structure - **DNA** contains four bases paired together: - Adenine (A) & Thymine (T) - Cytosine (C) & Guanine (G) #### Inheritance Diagrams - **Sex determination**: one of our 23 pairs of chromosomes determines our gender. - Females (XX) - Males (XY) #### Inherited Disorders | Disorder | Description | Dominant? | |---|---|---| | Polydactyly | Extra fingers and toes | Y | | Cystic Fibrosis | Cell membrane disorder | N | #### Mutations - Although in general, variation comes from genetic mixing (reproduction), mutations in DNA happen all the time. - Some mutations are beneficial and others can be bad, leading to cancer. #### Evolution - All species evolved from simple life forms. - **Natural selection**: characteristics which are preferable to the environment over time perpetuate through the species. - The species that have the favorable traits live longer and reproduce more frequently, meaning they are more successful. #### Selective Breeding - **Selective breeding** is the artificial selection of particular genetic characteristics. - Humans have been doing this for thousands of years. #### Examples of Selective Breeding - Disease resistance in food crops. - Animals that produce more meat, eggs or milk. - Domestic dogs with a gentle nature. - Large or unusual flowers. - **Inbreeding** can lead to little variation, making species more vulnerable to diseases. #### Genetic Engineering - It is **modifying the genome by introducing a gene from another organism**. #### Examples of Genetic Engineering - **Crops**: have been genetically engineered to resist diseases. - **Bacterial cells**: have been genetically engineered to produce useful substances instead of toxins, such as insulin. #### Concerns About Genetic Engineering - The main concern is that we haven't been doing it long enough to know the long-term effects on: - Insects and birds. - Human health. - Evolution itself. - Concerns are also expressed for social, political and religious reasons about it being unnatural and playing God. #### How Genetic Engineering is Done - **Enzyme**: used to isolate the gene. - **Gene**: is inserted into a vector, which could be a plasmid or a virus. - **Vector**: used to insert the gene into the required cell. - **Cell**: replicates. #### Cloning - Cloning is important for preserving rare plant species by taking and replicating **tissue culture**. - Cloning is also useful for quickly replicating garden plants by taking **cuttings**. - It is finally useful for replicating embryos in fertility treatment (separating when still stem cells), called **embryo transplants**. #### How Adult Cell Cloning Works. - **Nucleus** is removed from an unfertilized cell. - **Nucleus** is taken from another adult body cell. - **Adult body cell** is inserted into the empty egg cell. - An **electric shock** is applied to stimulate cell division. - The cell is **inserted into a womb**. - The cell develops into a **ball of cells**. #### Chapter 7: Ecology #### Communities - All plants and animals are well adapted to the interdependence and competition required of them when they live in a community. #### Animal Competition - Animals are competing for: - Food. - Mates. - Water. - Status. - Survival. #### Plant Competition - Plants are competing for: - Light. - Water. - Nutrients. - Territory. - Pollinators. #### Abiotic & Biotic Factors | Factor | Category | Examples | |---|---|---| | Non-living parts of the environment | Abiotic | Light intensity, temperature, moisture levels, pH, gas levels| | Living parts of the community | Biotic | Availability of food, new predators, new prey, new pathogens, competing species | #### Organisation - **Producers**: primary consumers (prey). - **Primary consumers**: eat producers. - **Secondary consumers**: eat primary consumers. - **Predators**: secondary consumers. #### Pyramids of Biomass - Approximately 10% of biomass energy is transferred to the next level on the pyramid. - The reasons biomass is lost: - Not all ingested material is absorbed - Some absorbed material is excreted - Energy is used in respiration #### Water Cycle - **Evaporation**: water changes from a liquid to a gas. - **Transpiration**: water evaporates from trees. - **Condensation**: water vapor turns into liquid water. - **Precipitation**: condensed water vapor falls to Earth. - **Percolation**: water flows into the soil and back to the oceans. #### Carbon Cycle - **Photosynthesis**: plants take in carbon dioxide and release oxygen. - **Respiration**: animals take in oxygen and release carbon dioxide. - **Combustion**: burning fossil fuels releases carbon dioxide. - **Decomposition**: decaying organisms release carbon dioxide. - **Mining**: fossil fuels containing carbon are removed from the Earth. #### Nitrogen Cycle - **Nitrogen-fixing bacteria**: in soil convert nitrogen gas into nitrates. - **Nitrates**: absorbed by plants. - **Plants**: convert nitrates into proteins. - **Animals**: feed on plants and obtain protein. - **Death & Waste**: when animals die or excrete waste, decay bacteria and fungi release ammonia into the soil. - **Denitrifying bacteria**: converts nitrates back into nitrogen gas. - **Lightning**: converts nitrogen gas into nitrates. #### How Humans are Affecting the Planet. #### Biodiversity - Our future depends on us keeping a large biodiversity on Earth. It helps to keep these ecosystems alive. #### Ways We are Reducing Biodiversity - **Waste**: Rapid growth in human population means rapid growth in waste. - This pollution occurs in water (sewage), soil (fertilizer) and air (smoke and acidic gases). - **Changes of land use**: Paired driveways, deforestation and urban centers are destroying habitats. #### How We Can Maintain Biodiversity - **Breeding programs**: - **Protection and regeneration**: Create margins and boundaries. - **Re-introduction**: reintroduce animals and plants to their former habitat. - **Reduction of impactful activities**: reduce our impact on the environment. - **Recycling resources**: reuse and recycle materials.