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Biology 1: free practice, theory and problems
All living things are made of cells. Cells take up nutrients, produce energy, build proteins and divide.
Contents
- The cell
- Heredity and genetics
- Ecology
- Evolution
- Photosynthesis and cellular respiration
- Biodiversity and classification
1. The cell
What is it about?
All living things are made of cells. Cells take up nutrients, produce energy, build proteins and divide.
Concepts
- Prokaryotic cells (bacteria) have no nucleus. Eukaryotic cells (plants, animals, fungi) have a nucleus and organelles.
- The mitochondria produce ATP by cellular respiration: glucose + oxygen → carbon dioxide + water + energy.
- The chloroplasts (in plants) carry out photosynthesis: carbon dioxide + water + light energy → glucose + oxygen.
- The plant cell has a cell wall, chloroplasts and a large vacuole, which the animal cell lacks.
- The cell membrane is a double layer of phospholipids with proteins. Substances pass by diffusion, osmosis or active transport.
2. Heredity and genetics
What is it about?
Genes are found in DNA and determine which proteins the cells make. In sexual reproduction, the offspring gets half its genes from each parent.
Concepts
- DNA consists of nucleotides with the bases A, T, C and G (A pairs with T, C with G).
- A gene is a piece of DNA that codes for a protein. Transcription: DNA → mRNA. Translation: mRNA → protein (in the ribosomes).
- Mitosis gives two identical cells (growth and repair). Meiosis gives sex cells with half the number of chromosomes.
- Alleles are variants of a gene. A dominant allele (A) masks a recessive allele (a).
- The cross Aa × Aa gives the ratio 1 AA : 2 Aa : 1 aa, i.e. a 25% probability of the recessive trait.
3. Ecology
What is it about?
Ecology is about the interactions between organisms and the environment they live in.
Concepts
- Producers (plants) make organic matter by photosynthesis. Consumers eat other organisms. Decomposers break down dead material.
- Food chain: grass → hare → fox. Food web: many chains linked together.
- Only about 10% of the energy passes from one trophic level to the next. The rest is used in cellular respiration and lost as heat.
- Matter cycles (carbon, nitrogen), while energy flows through the ecosystem.
- Carrying capacity: the largest population the environment can support over time.
4. Evolution
What is it about?
Evolution is change in the heritable traits of a population over generations. The main driving force is natural selection.
Concepts
- Variation: individuals in a population differ, partly because of mutations and sexual reproduction.
- Natural selection: individuals with traits that suit the environment well have more offspring, so these traits become more common.
- Adaptation: a trait that increases the chance of surviving and reproducing.
- Speciation often happens when populations become isolated from each other.
- Evidence for evolution: fossils, DNA similarities, homologous organs and observed evolution (for example antibiotic resistance).
5. Photosynthesis and cellular respiration
What is it about?
Nearly all the energy in almost every ecosystem comes from the Sun. Photosynthesis captures light energy and stores it in glucose. Cellular respiration releases the energy again and stores it as ATP, which the cells can use.
Concepts and formulas
- Photosynthesis (in the chloroplasts):
- Cellular respiration (in the mitochondria):
- The two processes are the reverse of each other, and together they make up a large part of the carbon cycle.
- Chlorophyll absorbs red and blue light and reflects green. That is why leaves are green.
- ATP is the cell's "energy currency". One glucose gives about 30–32 ATP with oxygen.
- Without oxygen: fermentation. Muscles make lactic acid, yeast makes ethanol and CO₂. Gives only 2 ATP per glucose.
- Factors that limit photosynthesis: light, CO₂ concentration and temperature.
Practise photosynthesis and cellular respiration in the app →
6. Biodiversity and classification
What is it about?
There may be 8–10 million species on Earth. To keep track of them, biologists sort them into groups by relationship. Biodiversity is the variety of genes, species and ecosystems, and it is under pressure.
Concepts and formulas
- Taxonomy: kingdom → phylum → class → order → family → genus → species.
- Scientific name: genus + species, for example *Homo sapiens* and *Canis lupus* (wolf).
- Three domains: bacteria, archaea and eukaryotes (plants, animals, fungi and protists).
- Biodiversity on three levels: genetic diversity, species diversity and ecosystem diversity.
- The biggest threats: land-use change (habitat loss), climate change, pollution, invasive species and overharvesting.
- The Red List shows species that are threatened in Norway.
- Keystone species: a species that many other species depend on, for example beavers or kelp forests.
Example problems with solutions
Here are some of the problems in biology 1. In the app, calculation problems get new numbers every time, so you can practise until it sticks – and take a graded practice exam before the real one.
The cell: What do prokaryotic cells lack?
Answer: A nucleus
Bacteria have DNA, but it lies freely in the cell, not in a nucleus.
Heredity and genetics: Which base pairs with A in DNA?
Answer: T
A–T and C–G. (In RNA, A pairs with U.)
Ecology: About how much of the energy passes from one trophic level to the next?
Answer: 10%
The rest is used for life processes and lost as heat.
Evolution: What is natural selection?
Answer: Individuals with favourable traits having more offspring
Individuals do not change themselves. It is the proportion of traits in the population that changes.