AQA GCSE Biology (Triple Science) - Infection, Response & Plant Biology

Comprehensive practice flashcards covering pathogens, communicable diseases, plant biology, immune responses, and drug development for AQA GCSE Biology (Triple Science).

What is a pathogen?

A microorganism that enters the body and causes infectious (communicable) disease (e.g., bacteria, viruses, protists, fungi).

What is the formula for calculating the total number of bacteria produced after a period of time?

$$\text{Total bacteria} = \text{Initial bacteria} \times 2^{\text{number of divisions}}$$

A bacterium has a division time of $30\,\text{minutes}$. How many bacteria will be produced from 1 single bacterium after $8\,\text{hours}$?

1. Divisions per hour: $\frac{60}{30} = 2$ times per hour. 2. Total divisions in $8\,\text{hours}$: $8 \times 2 = 16$ divisions. 3. Total bacteria: $1 \times 2^{16} = 65,536$ bacteria.

How do bacteria and viruses cause symptoms in the body differently?

Bacteria reproduce rapidly inside the body and release toxins that damage cells and tissues. Viruses live inside host cells, replicate using the cell's machinery, and cause the cell to burst, releasing new viruses.

What are the key details for Measles (type, symptoms, spread, complications, and prevention)?

Type: Virus.

Symptoms: Fever and a red skin rash.

Spread: Inhalation of droplets from coughs/sneezes.

Complications: Can cause blindness, brain damage (encephalitis), pneumonia, and can be fatal.

Prevention: Vaccination (MMR vaccine given to young children).

What are the key details for HIV / AIDS (symptoms, spread, treatment, and prevention)?

Symptoms: Starts with a flu-like illness; attacks immune cells until the body can't fight infections or cancers (late-stage HIV/AIDS).

Spread: Direct sexual contact, exchange of bodily fluids (sharing needles), unscreened blood transfusions, mother to child via breast milk. Treatment: Antiretroviral drugs (prevent virus replication).

Prevention: Condoms, screening blood, not sharing needles, HIV-positive mothers bottle-feeding.

What are the key details for Tobacco Mosaic Virus (TMV)?

Hosts: Tomatoes and tobacco plants.

Symptoms: Distinctive mosaic pattern of discolouration on leaves. Effect: Reduces chlorophyll $\rightarrow$ reduces photosynthesis $\rightarrow$ stunts growth and crop yield.

Spread & Prevention: Spread by direct contact or vectors

prevented by pest control, field hygiene, and using TMV-resistant plant strains.

What are the key details for Salmonella (cause, symptoms, spread, and prevention)?

Cause: Bacteria releasing toxins inside the body.

Symptoms: Fever, abdominal cramps, vomiting, diarrhoea (can be fatal due to dehydration).

Spread: Undercooked food, raw meat contamination.

Prevention: Keep raw and cooked food separate, don't wash raw chicken, wash hands/surfaces, cook chicken thoroughly, vaccinate poultry in the UK.

What are the key details for Gonorrhoea (cause, symptoms, complications, treatment, and prevention)?

Cause: Bacteria spread by unprotected sexual contact. Symptoms: Thick yellow or green discharge from vagina or penis, pain on urinating. Untreated Complications: Long-term pelvic pain, infertility, severe eye infections/blindness in babies born to infected mothers. Treatment: Antibiotics (though resistant strains exist; both partners must be treated). Prevention: Barrier contraception (condoms), reducing sexual partners.

What are the key details for Rose Black Spot (type, symptoms, spread, and treatment/prevention)?

Type: Fungus.

Symptoms: Purple or black spots develop on leaves; leaves turn yellow and drop early (weakens plant by reducing leaf area for photosynthesis).

Spread: Spores carried by wind or rain/drips of water.

Treatment/Prevention: Stripping/burning infected leaves, applying fungicides, breeding resistant strains.

What are the key details for Malaria (type, vector, symptoms, and prevention)?

Type: Protist parasite (reproduces sexually in female mosquito, asexually in human body).

Vector: Female Anopheles mosquito (needs blood meals to lay eggs), once it does protists enter the bloodstream

Symptoms: Recurrent episodes of fever and shaking when protists burst out of red blood cells.

Prevention: Insecticide-treated mosquito nets, insecticides, destroying mosquito breeding grounds (removing stagnant water), antimalarial drugs for travellers.

What are the human body's non-specific physical and chemical defences?

Skin , nose , trache and bronchi, stomach

Skin: Physical barrier, forms scabs, secretes antimicrobial substances.

Nose: Hairs and mucus trap airborne pathogens.

Trachea & Bronchi: Mucus traps pathogens; cilia waft mucus up to the throat to be swallowed.

Stomach: Hydrochloric acid kills pathogens swallowed in mucus or food.

How do aphids damage plants, and how can they be controlled?

Damage: Sharp mouthparts penetrate phloem vessels to suck sugar-rich sap, depriving the plant of nutrients and stunting growth. Prevention: Chemical pesticides, or biological pest control (releasing ladybirds to eat aphids).

What effects do Nitrate and Magnesium ion deficiencies have on plants?

Nitrate Deficiency: Nitrate is needed to convert sugars from photosynthesis into proteins $\rightarrow$ causes stunted growth. Magnesium Deficiency: Magnesium is needed to make chlorophyll for photosynthesis $\rightarrow$ causes yellow leaves (chlorosis).

What bacterial condition causes abnormal growths on plants?

Crown galls (bacterial infections in plants causing tumor-like growths).

What are the three main types of plant defence mechanisms (Physical, Chemical, Mechanical)?

Physical: Cellulose cell walls, tough waxy cuticle, bark/dead cell layers that fall off, leaf fall in autumn. Chemical: Antibacterial chemicals, poisons to deter herbivores. Mechanical: Thorns, hairy stems/leaves, leaves that droop/curl when touched, mimicry (looking like stones or egg-covered leaves).

What are the three roles of white blood cells in immune defence?

1. Phagocytosis: Engulfing and digesting pathogens. 2. Antibody production: Specific proteins produced by B-lymphocytes that bind to foreign antigens on pathogens. 3. Antitoxin production: Neutralising toxins produced by bacteria.

How does a vaccination lead to immunity?

1. Small quantities of dead or inactive pathogens are injected into the body. 2. White blood cells are stimulated to produce specific antibodies against the antigens. 3. White blood cells divide by mitosis to form memory cells. 4. If the live pathogen enters the body later, memory cells rapidly produce the correct antibodies to destroy it before you feel ill.

What is the difference between painkillers and antibiotics?

Painkillers (e.g., aspirin, paracetamol): Treat symptoms and relieve pain, but do not kill pathogens. Antibiotics (e.g., penicillin): Kill or inhibit the growth of bacteria without harming human body cells (cannot kill viruses because viruses live inside body cells).

What is antibiotic resistance and why is it a concern?

Mutations in bacteria allow some to survive antibiotic treatment. The resistant strain survives, reproduces, and increases in population (natural selection), making infections untreatable by standard antibiotics (e.g., MRSA).

Name three drugs originally extracted from plants or microorganisms and their sources.

1. Digitalis (heart drug): Extracted from Foxgloves. 2. Aspirin (painkiller): Extracted from Willow trees. 3. Penicillin (antibiotic): Extracted from Penicillium mould (discovered by Alexander Fleming).

What are the definitions of Efficacy, Toxicity, and Dosage in drug testing?

Efficacy: Whether the drug works to cure or prevent a disease. Toxicity: How safe or harmful the drug is (side effects). Dosage: The concentration of the drug that should be given and how often.

What are the three main steps involved in drug testing?

1. Preclinical (Lab): Tested on human cells, tissues, and whole organs. 2. Preclinical (Animals): Tested on live animals to check for side effects and how it works in a living organism. 3. Clinical Trials (Humans): Low doses given to healthy volunteers to test safety/side effects, tested on a small number of patients with the disease, and larger clinical trials to find the optimum dose.

Why are placebos, double-blind trials, and peer reviews used in clinical testing and research?

Placebo: A dummy drug (or existing standard treatment) used to control for the placebo effect and ensure comparison fairness. Double-blind trial: Neither the patient nor the doctor knows who gets the real drug or the placebo, preventing bias. Peer Review: Results are reviewed by independent scientists before publishing to prevent false claims.