Biology / Life Science: Cells, Systems, Inheritance and Ecosystems
What this domain covers
Grade 10 Biology in PNG moves from cell structure to whole organisms and ecosystems. Expect questions on organelles, movement of substances, photosynthesis and respiration, human digestion and circulation, reproduction and simple inheritance, and food webs.
Core rules and concepts
- The nucleus controls cell activity; mitochondria release energy by respiration; chloroplasts carry out photosynthesis; plant cells also have a cellulose cell wall and a large vacuole.
- Diffusion moves particles from high to low concentration. Osmosis is the movement of water across a selectively permeable membrane from a dilute solution to a more concentrated one. Active transport uses energy and can move substances against a concentration gradient.
- Photosynthesis: carbon dioxide + water -> glucose + oxygen, using light energy and chlorophyll. Respiration: glucose + oxygen -> carbon dioxide + water + energy. Respiration happens in all living cells all the time; photosynthesis only in cells with chlorophyll in light.
- Enzymes are specific biological catalysts. Amylase breaks starch to maltose, protease breaks proteins to amino acids, and lipase breaks fats to fatty acids and glycerol. High temperature or wrong pH denatures enzymes.
- In genetics, alleles are different forms of a gene. A dominant allele is expressed when present; genotype is the allele pair, phenotype is the visible trait.
Worked example
In pea plants, tall (T) is dominant over short (t). Cross a heterozygous tall plant (Tt) with a short plant (tt). The tall parent gives T or t; the short parent gives only t. Offspring are Tt, Tt, tt, tt. So the expected ratio is 2 tall : 2 short, or 1:1, and 50% are tall. The reasoning is that each parent contributes one allele per gamete, and the short parent has no dominant allele to pass on.
Traps that cost marks
Osmosis is not the diffusion of sugar or salt; it is water movement. Plants respire as well as photosynthesise. Respiration is a chemical reaction, not breathing. A dominant allele is not necessarily the most common allele in a population. Do not confuse genotype with phenotype.