Biology GCSE

Community

• Group of living interdependent organisms

• Plants produce food by photosynthesis (producers)

• Herbivores eat plants

• Insects pollinate plants

• Animals use plant and animal material to build nests and shelter

• Plants need nutrients from faeces and decay

Abiotic factors

Non-living elements of the environment

Interdependence

When different populations rely on each other to thrive and survive

Biotic factors

Interaction of living things

Habitat

An area where organisms live

Distribution

Where particular types of organisms are found within an environment

Ecosystem

interacting organisms and their environment

Abiotic factors affecting communities

• Light intensity

• Temperature

• Moisture levels

• Soil pH

• Wind intensity

• For aquatic organisms, oxygen availability

• CO² levels

Biotic factors affecting communities

• Food availability

• New pathogens or parasites could wipe out the population

• New predators

• Competition from other species

Trophic levels

• TL 1 - Producers that make their own food via photosynthesis (autotrophs)

• TL 2 - Primary consumers - herbivores that eat plants or algae

• TL 3 - Secondary consumers - carnivores that eat herbivores

• TL 4 - Tertiary consumers - carnivores that eat other carnivores. Apex predators have no predators

Biomass

the total dry mass of living organisms at each level in a food chain

How is biomass lost through TLs?

Biomass is lost through trophic levels due to metabolic processes and excretion. It is also lost as the animal cannot consume all of the dead one ie. bones, claws, hooves etc., and energy is used in respiration. Only a fraction of energy is passed on to the next level.

Arteries

Structure: Thick walls containing muscles and elastic fibers to withstand high pressure, narrow lumen.

Function: Carry oxygenated blood away from the heart to organs, except in the case of pulmonary arteries. They stretch with every heartbeat and have a lot of pressure.

Veins

Structure:Thinner walls than arteries with less muscle and elastic tissue, wider lumen, often assisted by valves to prevent backflow

Function: Carry deoxygenated blood away from the organs back to the heart, except for pulmonary veins. Do not have a pulse and have lower pressure compared to arteries.

Capillary

Structure: Very thin walls, only one cell thick, very small lumen

Function: Link the veins and arteries, enable substances like oxygen and glucose to diffuse out of your blood and into your cells easily

Double circulatory system

The circulation of blood from the heart to the lungs is separate from the circulation of blood to the rest of the body.

Benefits of Double circulatory system

• Blood pressure is higher, especially to the body

• Higher blood flow to the body tissues

• Oxygenated and deoxygenated blood flow separately

Heart

• A: Vena Cava

• B: Right atrium

• C: the valves

• D: Right ventricle

• E: Aorta

• F: Pulmonary artery

• G: Pulmonary vein

• H: Left atrium

• I: Left ventricle

Stent

• A metal mesh placed in a blocked or partially blocked artery. They are used to open up the blood vessel via the inflation of a tiny balloon

• Surgery is very easy to install✅

• Is effective most of the time ✅

• Can get stuck and block the artery or burst it ❌

• Quick recovery time✅

• Low risk of heart attack ✅

• Restore blood and last long ✅

• Can form blood clots and risk of infection ❌

Statin

• Drugs used to lower blood cholesterol and improve the balance of HDLs to LDLs

• Proven to reduce risk of heart attacks and strokes✅

• Muscle pain or weakness as common side effect ❌

• Increased risk of type 2 diabetes as can slightly raise blood sugar levels ❌

Platelets

• Small fragments of cells with no nucleus

• They assist with clotting progress as they get stuck in the mesh of fibres called fibrin when the skin is damaged

Plasma

• Transports blood components and dissolved substances - CO2 and digestion products

• Transports urea to kidneys for excretion and it is removed from the blood to make urine.

Red blood cells

• Bi-concave disc shape to maximise SA:V ratio for diffusion

• No nucleus for maximum haemoglobin capacity

White blood cells

• Form part of the body’s defence system against harmful microorganisms

• Some form antibodies, some form antitoxins, some consume pathogens

Bypass surgery adv+dis

• Very effective against severe blockages✅

• Higher infection risk ❌

• Long recovery time ❌

• Expensive ❌

• General anaesthetic needed

Valve replacements: Mechanical vs Tissue

Mechanical

• Last very long ✅

• Very effective and tough ✅

• Need to take medication for the rest of your life which prevents blood clotting ❌

Tissue

• No medication needed ✅

• Very effective ✅

• Only lasts 12-15 years ❌

• Big surgery ❌

Pacemaker

• Electrical device implanted to replace pacemaker cells

• Used to correct irregularities in the heart rate, implanted in the chest

• Sends strong, regular electrical signals to the heart to stimulate it to beat properly

• Some only activate when natural rhythm goes wrong

Cancer

• Disease caused by uncontrolled division (proliferation) of abnormal cells in a part of the body

Malignant tumours

• Invades neighbouring tissues and spread to other parts of the body via the blood

• Creates secondary tumours (metastases)

Benign tumours

• Growth of abnormal (slow growing) cells contained in one area

Health problems with tumours

• Can cause pressure or damage to an organ so can be fatal if the brain is involved as there is no space for the tumour to grow into

• Malignant tumour can cause serious health problems as can form secondary tumours and often completely disrupt normal tissue and if left untreated, will often kill the person

• Very difficult to treat

Communicable disease

A disease caused by pathogens that can be passed from one organism to another eg. HIV/AIDS, Salmonella, Cholera, COVID-19

Non-communicable disease

A non infectious disease that cannot be passed from one organism to another eg.Diabetes, Coronary heart disease, stroke, heart attack

Pathogen

A disease-causing microorganism (microscopic living thing)

Ways pathogens are spread - by water/food

• Diseases can be transmitted via infected water, raw or undercooked meat or contaminated food

• eg. diarrhoeal diseases, salmonella or cholera

By air (droplets)

• Transmitted from droplets expelled when breathing

• eg. influenza, tuberculosis or common cold

Direct contact

• An infected organism coming into contact with a healthy one via sexual or skin-to-skin contact

• eg. HIV, AIDS or hepatitis

Bacteria

• Bacteria can cause infection and illness

• Also in our body and are helpful, some decomposers

• Smaller than plant and animal cells but much larger than viruses

• Generally less than 10μm (micrometers)

• Living single-celled organisms

• Prokaryotic, without nucleus

• Mostly treatable with antibiotics

Viruses

• Very small, ~20-200nm (nanometers)

• Not classified as living organisms

• Only have protein coating and genetic material inside, coating is instead of the cell membrane

• Double or single strand DNA or RNA

• Cannot be treated

Fungi

• Range from 2-80μm

• Most common route of infextion is via inhalation of spores which cause respiratory infections

• Most commonly reproduce asexually but can reproduce sexually

• eg. ringworm, athlete’s foot, fungal nail

Preventing infections - Hygiene

Measures include handwashing at certain times, using disinfectants on dirty surfaces, keeping raw meat separate, coughing or sneezing in tissues and maintaining hygiene of people and agricultural machinery

Isolation

If someone has an infectious disease, they should be kept on their own away from uninfected people to prevent the spread of the disease to more vulnerable people

Destroying/controlling vectors

• Some diseases are passed on through vectors like mosquitoes or houseflies

• If they are destroyed, it can prevent the spread of disease

Vaccination

• This is done by introducing a small, harmless amount of a disease to your body so your immune system knows how to quickly fight and overwhelm the disease before it can cause damage

Measles

• Enters from nose, mouth and eyes

• Immune system responds intitially with natural killer cells

• Infects dendritic cells and uses them to enter deeper into the body

Symptoms of measles

• High fever, rash, headache and bronchitis

• Spreads easily and destroys the immune system

• Long term effects include very weak immune system taking long to recover

Skin defences

• Physical barrier to prevent pathogens from reaching tissues underneath

• If skin is breached, it can leave the body exposed but recovers quickly using platelets, also prevents severe blood loss

• Produces antimicrobial secretions to destroy pathogens

• Covered with extra microorganisms as and extra barrier

Antibiotics

• Inhibit cell wall synthesis

• Interrupt DNA/RNA synthesis

• Disrupt protein production by blocking ribosome action

• Damage cell membranes

Monoclonal antibodies

• Produced in a lab and made from a single clone of immune cells

• Cloned immune cells are identical and so are the antibodies they produce

• Specific to one binding site on one protein (antigen) and so are able to target a specific chemical/cells

+ and - of MAbs

• Very high specificity ✅

• Can be used to diagnose diseases ✅

• Cancer treatments/therapy ✅

• Time consuming❌

• Expensive ❌

• Ethical concerns ❌

• Side effects ❌

• Can be too specific as it only targets 1 disease/1 person❌

Hybridoma

A cell created during the production of MAbs by the fusion of an antibody-specific lymphocyte and a tumour cell

Uses of MAbs - Pregnancy tests

• Reliant on MAbs that bind to HCG hormone that is produced in early stages of pregnancy

• MAbs in pregnancy test bind to the hormone if its present and produce colour change

• Small amounts of the hormone are passes through urine

Disease diagnosis

• Eg. Used in blood test for prostate cancer

• Becoming more important in modern disease detection

• Made to bind to specific antigens, on blood clots or cancer cells

• MAbs carry markers to help see doctors where disease has spread

Measuring and monitoring

• Used in hospitals and labs to measure hormone levels and other chemicals in the blood

• Eg. donated blood for HIV infection, detecting illegal athlete drug use

Disease treatment

• Can be used to treat specific diseases

• Used to trigger immune responses, carry toxic drugs for chemo or to block receptors on cancer cells

• Used to treat cancers

Research

• Used to identify or locate specific molecules in a cell/tissue

• MAbs linked a molecule of fluorescent dye can be used to observe build up of disease or cancer

How MAbs are made

1. Mouse lymphocytes stimulated by introducing the antigen by injection

2. Lymphocytes extracted from mouse’s spleen

3. Lymphocytes combined with a tumour cell (myeloma cell)

4. Hybridoma cell made so the tumour cell divides quickly but can still make the antibody

5. A single hybridoma cell can be cloned to produce many identical cells that all produce the same antibody

6. A large amount of the antibody can be collected from mouse’s spleen   

Uses of monoclonal antibodies

• Direct use of MAbs to trigger the immune system to recognise, attack and destroy cancer cells

• MAbs can be used to carry toxic drugs or radioactive substances for radiation therapy, or chemicals that stop cells growing and dividing to attack the cancer cells directly without harming other cells in the body

• Using MAbs to block receptors on the surface of cancer cells and so stop the cells growing and dividing

Pregnancy test process

1. Urine applied

2. Reaction zone - Mobile Abs specific to HCG here, can move and have dye attached

3. Result window - Immobilised Abs specific to HCG

4. Control window - Immobilised Abs specific to mobile Abs from reaction zone

• No line in result or control - INVALID

• Line only in control window - NEGATIVE

• Line in control and result window - POSITIVE

Synthetic vs Plant antibiotics

Synthetic

• Can be manufactured on a larger scale more easily so more product can be manufactured

• Easier to edit for fewer side effects

• More stable and dosage can be controlled

• Safer for rigorous testing of synthetic drugs

Plant

• Only small amounts of active chemical can be found

• Plant extracts can be impure

Antibiotics from living organisms

• Evidence of medicinal properties means a lot less time and expenses for research ✅

• Long term usage suggests few side effects✅

• More biodegradable - less harmful environmental effects✅

• Sourcing the living material may be difficult (eg. low yield, low availability etc.) ❌

• Concentrations may be low❌

• Might be difficult isolating the chemical that has the antibiotic effect❌

Developing drugs

1. In-vitro testing - New drugs tested on cells, tissues and organs. Many drugs fail at this point.

2. Animal testing - Tested on animals to see how they work in whole living organisms. Side effects and dosage established here. Done one rabbits, mice, monkeys

Human testing

1. Phase 1 - Testing on a small number of healthy male volunteers. Very low doses are used

2. Phase 2 - Testing on a small number of humans with the disease. It determines if the drug is safe and effective.

3. Phase 3 - Similar to Phase 2 but much larger numbers are used

Approval and publishing results

• Results of tests and trial published in journals after have been peer reviewed - other scientists working in same field check results

• If tests are passed, drug is licensed and doctors can begin using it

• Drug is monitored when in use and checked by NICE (National Institute for Clinical Excellence)

Placebo

A medicine that doesn’t contain the active drug, used in clinical trials of new drugs

Double blind trial

Neither researcher or patient know who has had the real medicine or the placebo

Detecting diseases in plants

• Malformed stems and leaves (due to aphid infestation)

• Stunted growth (eg. nitrate deficiency)

• Spots on leaves (rose black spot)

• Decay or rotting (rose black spot)

• Growth (eg. crown galls)

• Discolouration (yellowing in Mg deficiency)

• Presence of visible pests (aphids, caterpillars)

Plant diseases - Virus

• Eg. Cauliflower/ tobacco mosaic virus

• Symptoms - Mosaic patterns, vein clearing, stunted growth

• Virus destroys cells, reducing plant growth because the affected areas of the leaf do not photosynthesise

Bacteria

• Eg. Crown gall

• Symptoms - Abnormal galls (rough tumours) on the roots, trunk or crown of a plant

• Galls can encircle stem or trunk, cutting off flow of sap to cause stunted growth and eventual death  

Fungus

• Eg. rose black spot

• Black spots on leaves become larger blotches and then leaves turn yellow and fall off

• Causes defoliation and weakening of the plant, reducing its ability to flower and makes it more susceptible to other diseases

Parasitic

• Eg. root knot nematodes

• Damaged roots

• Prevents the plant getting the water and mineral ions it needs so it fails to grow

Insects

• Eg. aphids

• Discoloration, leaf curling, yellowing, stunted growth, visible green insects around stem

• Sharp mouth parts penetrate phloem vessels to feed on sugar rich sap, damaging and weakening the plant, aphids also act as vectors 

Nitrate ion deficiency

• Stunted growth

• Nitrate ions not present to convert the sugars made in photosynthesis into proteins needed growth

Magnesium ion deficiency

• Leaves turn yellow between veins but veins remain green, called interveinal chlorosis

• Mg ions not present to make chlorophyll so leaves become yellow and growth slows as plant cannot fully photosynthesise

Identifying plant diseases

• Testing kits using MAbs

• Taking samples to a lab

• Gardening manuals or online manuals

Plant defences - Chemical

• Chemicals that the plant can secrete

• Lots of medicines are derived from plants, like aspirin from willow bark or caffeine

• Poisons

• Anti-microbial chemicals

Physical defences

• Physically prevent entry of pathogens

• Layers of dead cells eg. bark

• Cellulose cell walls

• Waxy cuticle on leaves and stems

Mechanical defences

• Similar to physical but more of a function rather than just a barrier

• Leaves that curl up/ droop when touched

• Thorns/ hairs stop animals eating or touching  

Photosynthesis

• 6CO₂ + 6H₂O —> C₆H₁₂O₆ + 6O₂

 reactants                       products

• Carbon dioxide + Water —> Glucose + oxygen

                                 Light and chlorophyll

• Endothermic reaction as it takes in energy from the environment

Chloroplasts

Organelles of plant cells that contain a green substance called chlorophyll

Chlorophyll

Absorbs light energy and this is transferred into chemical form in glucose molecules

Optimum conditions for plant growth

• Lots of sunlight

• Warm temperature, not too hot as enzymes would denature

• High CO₂ concentration

• if one of these is in short supply, we call this a limiting factor

RoP graph for CO₂ concentration

RoP grpah for light intensity 

RoP graph for temperature

Hydroponics

A method of growing plants using mineral nutrient solutions in water without soil in order to optimise growth rate

Uses of glucose

• Can be converted into fats and oils for storage

• Converted into proteins for plant growth

• Stored as starch for storage

• Used as an energy source for respiration

• Used to make cellulose in plant cell walls

Aerobic respiration

• glucose + oxygen —> carbon dioxide + water + (release of energy)

• C₆H₁₂O₆ + 6O₂ —> 6CO₂ + 6H₂O (energy transferred to the environment)

• Site of aerobic respiration is the mitochondria

• Inner membrane is folded to increase SA for enzymes involved in aerobic respiration

• Respiration is an exothermic reaction as it releases energy to the surroundings

Respiration

• Allows you to keep warm

• To carry out the basic functions of life

• To make your muscles contract

Respiration in plants

• Energy released from respiration is required to move mineral ions, such as nitrates from the soil into the roots

• Plants can synthesise amino acids from glucose and nitrate ions

• They can absorb nitrates from the soil and ‘fix‘ atmospheric nitrogen

Anaerobic respiration

• An exothermic reaction in which glucose is broken down in the absence of oxygen to produce lactic acid in animals and ethanol and CO₂ in plants and yeast

• A small amount of energy is transferred for the cells

• C₆H₁₂O₆ —> 2C₃H₆O₃ + ENERGY

• glucose —> lactic acid (energy transferred to the environment)

• IN PLANTS - glucose —> ethanol + carbon dioxide (energy transferred to the environment)

Lactic acid

The end product of anaerobic respiration in animal cells

Oxygen debt

The extra oxygen that must be taken into the body after exercise has stopped to complete the aerobic respiration of lactic acid

Response to exercise

Hormones

Short term effects of exercise

• Heart beats faster in order to pump more blood around the body to deliver more oxygen and glucose to cells to release energy via respiration

• Breathing gets heavier to get more oxygen into the bloodstream

Long term effects of exercise

• Increased heart and lung volume

• Resting pulse and breathing rate lowers

• Cardiac output (amount of blood pumped per beat) increases

Metabolism in plants and animals

• Formation of lipids from glycerol and fatty acids🐵

• Respiration🐵

• Breakdown of excess protein into urea 🐵

• Conversion of glucose—>glycogen🐵

• Conversion of glucose—> starch🌱

• Synthesis of protein from glucose and nitrate ions🌱

Metabolism

• Sum of all reactions that take place in a cell or the body

• Affected by

  • Age

  • Muscle to fat ratio

  • Hormones

  • Genetic factors

DNA and the genome

• Genome is the entire genetic material of an organism

• Human Genome Project sequenced every gene in the human body

• DNA provides chemical instructions about how to build an organism

Mitosis

1. Interphase - DNA replicates to form two copies of each chromosome

2. Cell grows and double the organelles

3. Mitosis - Prophase - Chromosomes condense to become more visible and membrane around nucleus disappears

4. Metaphase - Chromosomes line up along middle of the cell

5. Anaphase - One copy of each chromosome is pulled to each end of the cell

6. Telophase - A new nuclear membrane forms around each set of chromosomes

7. Cytokinesis - Cytoplasm and cell membrane divide to form 2 identical daughter cells

Stem cells

Unspecialised cells that have not yet differentiated into a specific role, have the capacity to become any type of cell

Stem cells in plants

• Cell division in plants take place in regions of the plant called meristems. These tissues are found in the tips of roots and shoots

• Plants only get taller when cells in meristems elongate following cell division

• After this cells differentiate into their final form

Re-differentiation

Plant cells can become a different specialised cell, even after they have first differentiated