Important Knowledge Organizers for WJEC GCSE Biology Unit 2

Disease, Defence and Treatment

Ever wondered how scientists create targeted treatments that can find specific diseases in your body? Monoclonal antibodies are like biological detectives - they're identical antibodies created in labs that can hunt down particular antigens (foreign substances).

The process is quite clever: scientists inject a mouse with a specific antigen, wait for the mouse's immune system to produce antibodies, then fuse one antibody-producing cell with a tumour cell. This creates a hybridoma that can divide endlessly, producing millions of identical antibodies.

These lab-made antibodies have loads of practical uses. They can detect infections like HIV, Chlamydia, or malaria in blood samples, help match organ donors to recipients, and even carry cancer drugs directly to tumour cells. They're also brilliant for tracking disease outbreaks in communities.

Antibiotics like penicillin work differently - they destroy bacteria or stop them growing, but they're useless against viruses. Alexander Fleming discovered penicillin by accident when he noticed a fungus killing bacteria in his lab. The big worry now is antibiotic-resistant bacteria like MRSA, which is why doctors are more careful about prescribing antibiotics and hospitals focus heavily on hygiene.

Quick Tip: Remember that antibiotics only work on bacteria and fungi - never on viruses like the common cold!

Micro-organisms and Their Applications

Working with microorganisms is like cooking - contamination ruins everything! Scientists use aseptic technique to keep their experiments clean and safe.

The key steps include sterilising all equipment, using an inoculating loop heated to red-hot in a flame, and only lifting Petri dish lids slightly to prevent airborne contamination. School labs incubate cultures at 25°C for 24-48 hours - this temperature encourages growth without creating dangerous pathogens.

When counting colonies, you need between 20-200 colonies on each plate for reliable results. Fewer than 20 isn't statistically meaningful, and more than 200 creates clumping that makes counting impossible.

Temperature controls microbial growth, which is why food storage matters so much. Room temperature allows rapid bacterial growth, refrigerators slow it down, and freezers stop it completely. Fermenters create perfect growing conditions for useful microorganisms like the Penicillium fungus that produces penicillin, providing optimal pH, temperature, oxygen, and nutrients.

Lab Safety: Always sterilise equipment before and after use - this protects both your experiment and the environment!

Role of Kidney in Homeostasis

Your kidneys are incredible biological filters that clean about 180 litres of blood every day! The excretory system removes urea (a toxic waste product) and regulates your body's water content.

Each kidney contains about a million tiny filtering units called nephrons. Blood enters through the renal artery, gets filtered in the Bowman's capsule under pressure, then useful substances like glucose get reabsorbed back into the bloodstream. The hormone ADH controls how much water gets reabsorbed, helping maintain perfect water balance.

When kidneys fail, you've got two main treatment options. Dialysis involves connecting to a machine several times a week that filters your blood artificially - it's immediately available but seriously restricts your lifestyle. Kidney transplants can last 12-15 years and give you much more freedom, but finding a matching donor is difficult and you'll need immunosuppressive drugs for life.

Doctors can detect kidney problems and diabetes by testing urine. Red blood cells in urine suggest kidney damage, while glucose indicates possible diabetes.

Did You Know?: The dialysis machine uses counter-current flow to maintain concentration gradients - the same principle used in fish gills!

Variation and Evolution

Why don't you look exactly like your siblings? It's all about variation - the differences between members of the same species caused by genetic factors, environmental influences, or usually both.

Sexual reproduction involves two parents and creates offspring with genetic variation, making species more likely to survive environmental changes. Asexual reproduction uses just one parent, producing genetically identical clones quickly but with no variation.

Evolution by natural selection explains how species change over time. Charles Darwin and Alfred Wallace figured out this process: random mutations create variation, organisms compete for survival, those with advantageous traits survive better, and they pass these beneficial genes to their offspring.

Continuous variation (like height and weight) is controlled by multiple genes plus environmental factors. Discontinuous variation (like blood type) is usually controlled by single genes, creating distinct categories.

Cystic fibrosis demonstrates genetic inheritance - if both parents carry the recessive gene, there's a 25% chance their child will have the disease. Gene therapy can treat this by delivering normal genes to lung cells, though it's currently a treatment rather than a cure.

Evolution Insight: Environmental changes that happen too quickly for natural selection can lead to extinction - that's why climate change is such a concern for biodiversity!

DNA and Inheritance

DNA is basically a biological instruction manual written in a four-letter alphabet: A, T, G, and C. These bases pair up in a specific way (A with T, G with C) to form the famous double helix structure.

Every three bases form a triplet code that specifies which amino acid to use when building proteins. This is how your DNA controls everything from your eye colour to how your body fights infections.

Genetic crosses help us predict inheritance patterns using Punnet squares. Dominant alleles (capital letters) show up in your appearance whenever present, while recessive alleles (lowercase letters) only appear when you inherit two copies.

Genetic profiling cuts DNA into fragments that create unique patterns - like biological fingerprints. This technology helps solve crimes, establish paternity, and identify disease genes, though it raises important ethical questions about privacy.

Genetic modification allows scientists to transfer useful genes between organisms. This can create crop plants resistant to diseases or herbicides, potentially increasing food production. However, concerns exist about creating "super weeds" and unknown long-term effects.

Sex determination in humans depends on the 23rd chromosome pair - females have XX, males have XY. Each fertilisation has a 50% chance of producing either sex.

Inheritance Tip: In a cross between two heterozygous parents, expect a 3:1 ratio of dominant to recessive traits in the offspring!

Cell Division and Stem Cells

Your body contains trillions of cells, all descended from a single fertilised egg through carefully controlled cell division. Chromosomes are like filing cabinets containing your genes, with each chromosome carrying hundreds of different genes.

Mitosis is the type of cell division used for growth and repair. It produces two identical daughter cells with the same number of chromosomes as the parent cell. When mitosis goes wrong and becomes uncontrolled, it causes cancer.

Meiosis is completely different - it only happens when making sex cells (gametes). This process reduces chromosome number by half and creates genetic variation through shuffling genes between chromosomes. That's why you're genetically unique (unless you're an identical twin!).

Stem cells are the ultimate biological multitaskers - undifferentiated cells that can become any other cell type. Embryonic stem cells are the most versatile, while adult stem cells are more limited but avoid ethical concerns.

Using your own stem cells for treatment is ideal because there's no rejection, no need for tissue typing, and no requirement to find donors. This makes stem cell therapy incredibly promising for treating conditions like Parkinson's disease, diabetes, and spinal cord injuries.

Medical Marvel: Stem cell research could revolutionise medicine by allowing us to grow replacement organs and tissues in the lab!

Classification and Biodiversity

Scientists organise life using a hierarchical system that groups organisms from broad categories down to specific species. The binomial system gives every species a two-part scientific name (like Homo sapiens for humans) that's universal - no confusion from different languages or local names.

Adaptations help organisms survive in their environments. These can be physical (like a fennec fox's large ears for heat loss) or behavioural (like being nocturnal to avoid desert heat). Arctic foxes show the opposite adaptation with small, furry ears to conserve heat.

All organisms face competition for limited resources. Animals compete for food, territory, and mates, while plants compete for light, water, and minerals. Interspecific competition occurs between different species, while intraspecific competition happens within the same species.

Biodiversity measures both the variety of species and their numbers in an area. It's crucial because it provides food, medicines, industrial materials, and enhances human wellbeing. We protect biodiversity through national parks, seed banks, and international agreements like CITES.

Scientists measure plant biodiversity using quadrats - square frames thrown randomly to sample areas without bias. Taking larger samples gives more valid estimates of species numbers and distribution patterns.

Conservation Fact: Maintaining high biodiversity isn't just about protecting cute animals - it's essential for human survival and discovering new medicines!