Romania Clasa a IX-a Biology

1. Science as a process

Scientific method and research ethics · Advanced investigation (CS)

• The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.

2. The cell: structural and functional unit of life

Molecules of life · Roles of biomolecules (CS) · The cell · Cell biology extension (CS)

• Biomolecules – A cell is mostly water, plus four big families of carbon compounds: proteins, carbohydrates, lipids and nucleic acids. Grinding tissue in acid separates small molecules (acid-soluble pool) from big ones – proteins, polysaccharides and nucleic acids (acid-insoluble pool). Proteins are chains of amino acids folded into four levels of structure. Polysaccharides are chains of sugars; lipids are fatty acids on glycerol; nucleic acids are chains of nucleotides. Enzymes are protein catalysts that bind a substrate at the active site, lower the activation energy, and are affected by temperature, pH, substrate level and inhibitors.
• Enzymes – Enzymes are proteins that act as biological catalysts: they speed up reactions in cells without being used up. Each enzyme has an active site that fits only one kind of substrate (specificity). Enzymes work by lowering the activation energy. They work best at an optimum temperature and pH; too much heat or the wrong pH changes the active site's shape and denatures them.
• The Cell: Basic Unit of Life – Every living thing is made of cells. Robert Hooke first saw cells in cork in 1665. Cells are prokaryotic (no true nucleus, like bacteria) or eukaryotic (true nucleus). Plant cells have a cell wall, chloroplasts and a big vacuole; animal cells do not. Each organelle has a job. Water enters and leaves cells by osmosis. Cells make new cells by mitosis (growth) and meiosis (sex cells).
• Cell Cycle and Cell Division – A cell grows, copies its DNA and splits in a fixed order called the cell cycle: interphase (G1, S, G2) and M phase. In S phase the DNA doubles (2C → 4C) but the chromosome number stays the same. Mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis give two cells identical to the parent – it is an equational division used for growth and repair. Meiosis has two divisions; in meiosis I homologous chromosomes pair, cross over and separate, halving the chromosome number (2n → n). It makes four haploid cells for gametes and creates variation.

3. Levels of integration and organisation of life

Levels of organisation · Biotope and populations (CS)

• Levels of Organisation: From Cell to Biosphere – Life is built in levels, like a set of boxes inside boxes. Cells join into tissues, tissues into organs, organs into organ systems, and organ systems into a whole organism. Organisms of one species form a population; many populations form a community; a community plus its non-living surroundings is an ecosystem; all ecosystems together make the biosphere. Each level is made of the level below it and can do things the lower level cannot.

4. Diversity and conservation of life

Tree of life and classification · Prokaryotes: Bacteria and Archaea · Eukaryota: protists, algae, fungi · Plants · Animals · Health education: parasites and vectors · Value and conservation of biodiversity

• Diversity and Classification of Living Organisms – Earth has millions of kinds of living things, and India is one of the richest places. To study them, we sort them into groups by asking simple questions about their bodies: Is there a nucleus? One cell or many? Can it make its own food? This gives five kingdoms: Monera, Protista, Fungi, Plantae and Animalia. Animals split into invertebrates and vertebrates. Every species gets a two-part scientific name. Viruses are not cells, so they fit in no kingdom.
• Biological Classification – Whittaker (1969) sorted living things into five kingdoms, Monera, Protista, Fungi, Plantae and Animalia, using cell type, cell wall, body plan, mode of nutrition, reproduction and relationships. Monera are prokaryotes (bacteria, archaebacteria, cyanobacteria, mycoplasma). Protista are one-celled eukaryotes in five groups. Fungi are heterotrophs with chitin walls in four classes. Lichens are an alga and a fungus living together. Viruses, viroids and prions are not placed in any kingdom.
• Plant Kingdom – The plant kingdom climbs a ladder of new features. Algae are simple, mostly water plants with no roots or stems. Bryophytes (mosses) live on damp land but have no vascular tissue. Pteridophytes (ferns) are the first with xylem and phloem. Gymnosperms carry naked seeds. Angiosperms hide seeds inside fruits and have flowers. In all of them, a haploid gametophyte and a diploid sporophyte take turns: alternation of generations.
• Animal Kingdom – Animals are sorted using a few body-plan questions: level of organisation, symmetry, number of germ layers, type of body cavity (coelom), segmentation and presence of a notochord. These give 11 major phyla: Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata and Chordata. Chordates have a notochord, a dorsal hollow nerve cord and gill slits at some stage; vertebrates among them fall into seven classes from jawless fish to mammals.
• Biodiversity and its Conservation – Biodiversity is the variety of life at three levels: genetic, species and ecological. It is highest near the equator and grows with area (log S = log C + Z log A). Every species matters, like rivets on a plane. We are losing species fast because of the 'evil quartet': habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinction. The IUCN Red List (Red Data Book) ranks species from Least Concern to Extinct. We protect life in situ (hotspots, national parks, sanctuaries, biosphere reserves, sacred groves, Ramsar wetlands) and ex situ (zoos, botanical gardens, seed and gene banks).

5. Human impact on ecosystems

Humans in the modern environment

Coming soon