Poland Szkoła podstawowa, klasa VIII Biology

1. V. Genetics

DNA, chromosomes and cell division · Cancer as uncontrolled division · Inheritance · Mutations and genetic diseases

• Cancer: When Cells Forget to Stop Dividing – Our body makes new cells by mitosis only when needed: to grow, to heal or to replace worn-out cells. Genes in DNA control this: proto-oncogenes act like an accelerator (go), tumour-suppressor genes like a brake (stop), and other genes repair DNA or make a damaged cell self-destruct (apoptosis). Cancer starts when mutations build up in these genes in one cell. The cell ignores stop signals and divides again and again (1, 2, 4, 8…), forming a lump called a tumour. A benign tumour stays in one place inside a capsule; a malignant tumour invades nearby tissue and can spread through blood or lymph to other organs (metastasis). Mutations come from carcinogens (tobacco smoke, UV light, X-rays and other radiation, some chemicals and air pollution), some viruses (HPV, hepatitis B), lifestyle (alcohol, obesity, poor diet, inactivity), from copying errors with age, and some are inherited (for example BRCA genes). Many cancers can be prevented (no tobacco, sun protection, HPV and hepatitis B vaccines, healthy diet, exercise) and treated well if found early (screening, surgery, chemotherapy, radiotherapy, targeted therapy and immunotherapy).
• Heredity and Mendel's Laws – Heredity is the passing of traits from parents to children through genes. Each parent gives one copy of every gene. A dominant copy hides a recessive one, which is why Mendel saw 3:1 in a monohybrid cross and 9:3:3:1 in a dihybrid cross. Genes are pieces of DNA that make proteins, and proteins build the trait.
• Mutations – A mutation is a sudden, lasting change in the DNA. Gene (point) mutations change one or a few bases: substitution, insertion or deletion. Insertions and deletions shift the reading frame. Chromosome mutations change big pieces or the number of chromosomes. Mutations happen by chance or because of mutagens such as UV light, X-rays and some chemicals. They can be harmful, neutral or useful, and they are the first source of all genetic variation.

2. VI. Evolution of life

Evolution and selection

• Evolution: How New Kinds of Living Things Arise – Variations arise during reproduction. Nature selects those that help survival, so over many generations populations change: this is evolution. Only inherited (DNA) changes pass on; acquired changes do not. Separated populations can become new species. Homologous organs, analogous organs and fossils help us trace who is related to whom, and complex organs evolved step by step.

3. VII. Ecology and environmental protection

Ecosystems and populations · Interactions between species · Food chains and energy flow · Tolerance, resources and human impact

• Ecosystem, Food Chains and Energy Flow – An ecosystem is all the living things in a place plus the non-living things around them, working together. Energy enters as sunlight, passes one way up a food chain, and only about 10% moves to each next level.

4. VIII. Threats to biodiversity

Protecting biodiversity

Coming soon