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The nature and variety of living organisms

Characteristics of living organisms

1.1 - Characteristics of living organismsBiology studies living organisms, so the first question is how to recognise that something is alive. Pearson Edexcel does not ask for one magic test. It asks you to understand the shared life processes that living organisms carry out: nutrition, respiration, excretion, response, movement, control...

Variety of living organisms

1.2-1.4 - Classifying organisms and pathogensBiologists classify organisms by looking for shared features, especially cell structure, nutrition, storage carbohydrates and examples of disease-causing forms. In this lesson, you will use the Edexcel groups plants, animals, fungi, protoctists, bacteria and viruses exactly as they are used in th...

Structure and functions in living organisms

Level of organisation and cell structure

2.1-2.4 - Organisation and cell structuresLiving organisms are built in levels: tiny structures inside cells help cells work, and cells can work together in larger structures. This lesson focuses on the Edexcel plant and animal cell structures you need to recognise, describe and compare. The key exam skill is to link each named structure...

2.5B-2.6B - Cell differentiation and stem cellsMulticellular organisms are not just large collections of identical cells. During development, cells become specialised so different parts of the organism can do different jobs. Stem cells matter because they can divide and produce cells that may replace damaged or diseased cells, but using them...

Biological molecules

2.7-2.9 - Biological molecules and food testsFood is made from large biological molecules, and those molecules are built from smaller units. In this lesson you will learn the element patterns and building blocks that Edexcel expects you to recall, then use qualitative food tests to identify glucose, starch, protein and fat in food samples.

2.10-2.12 - Enzyme action and temperatureEnzymes make metabolic reactions happen fast enough for living organisms to survive. This lesson shows how enzymes act as biological catalysts, why their active sites matter, how temperature changes enzyme activity, and how to investigate that effect in a practical.

2.13-2.14B - Enzyme activity and pH practicalEnzymes work because their active sites have a particular shape. This lesson shows how changing pH can alter that shape, then uses a practical investigation to measure the effect of pH on enzyme activity. The practical model is amylase digesting starch, with iodine solution used to show when star...

Movement of substances into and out of cells

2.15-2.17 - Diffusion, osmosis and active transportCells are surrounded by membranes, so useful substances must be able to enter and waste substances must be able to leave. Some movement happens passively down a gradient, while some needs energy from the cell. This lesson compares diffusion, osmosis and active transport, then uses those ideas to...

Nutrition

2.18-2.20 - Photosynthesis reactions and limiting factorsPhotosynthesis is the process that lets flowering plants trap light energy and store it as chemical energy in glucose. In this lesson, the process is treated as an energy conversion, a pair of equations, and a set of rate patterns. The key exam skill is to connect the graph shape to the factor th...

2.21-2.23 - Leaf adaptations, minerals and photosynthesis practicalLeaves are not just flat green surfaces: their layers, air spaces and transport tissues make photosynthesis efficient. Plants also need mineral ions to build the molecules that let them grow. This lesson finishes with the practical logic for showing oxygen production, starch production, and the r...

2.24-2.26 - Balanced diet and energy requirementsA balanced diet is not a diet where every food component is eaten in equal amounts. It is a diet that supplies the right nutrients, in suitable proportions, for the body's needs. Those needs change with the person's activity level, age and pregnancy, so "balanced" always means matched to the indi...

2.27-2.28 - Alimentary canal and peristalsisFood does not just sit inside the body while it is digested. It passes through a muscular tube called the alimentary canal, where different regions carry out different jobs. This lesson follows the route food takes and then explains the muscle action that keeps it moving.

2.29-2.32 - Digestive enzymes, bile and absorptionFood is useful to the body only after large, insoluble molecules have been digested into small, soluble molecules. Digestive enzymes do the chemical breakdown, bile makes lipid digestion more efficient, and the small intestine absorbs the soluble products into transport systems. This lesson follo...

2.33B - Food energy practicalFood contains chemical energy. In this practical, you estimate how much energy a food sample releases by burning it and measuring how much it warms a known mass of water. The method is simple, so the result is an estimate rather than the true food-label value, but it is excellent for learning fai...

Respiration

2.34-2.37 - Aerobic respiration and ATPRespiration is the chemical process that transfers energy from glucose into ATP in living organisms. ATP is the small molecule cells can use directly when they need energy for work such as movement, active transport, and building larger molecules. In this lesson, the main focus is aerobic respira...

2.38 - Anaerobic respirationAnaerobic respiration releases energy from glucose when oxygen is not available. For this lesson, the key skill is to know the word equation in animal cells and the word equation in plant cells. The reactant is the same each time, but the products are different, so the organism named in the quest...

2.39 - Respiration practicalRespiring living organisms release carbon dioxide and heat. In this practical, you investigate those two products using living material such as germinating seeds, then compare the results with suitable controls. The exam focus is not just the observation: it is also whether the method is fair, re...

Gas exchange

Transport

Excretion

Co-ordination and response

Reproduction and inheritance

Reproduction

Inheritance

Ecology and the environment

The organism in the environment

Feeding relationships

Cycles within ecosystems

Human influences on the environment

Use of biological resources

Food production

Selective breeding

Genetic modification (genetic engineering)

Cloning

2.38 - Anaerobic respiration

2.38 - Anaerobic respiration

Anaerobic respiration releases energy from glucose when oxygen is not available. For this lesson, the key skill is to know the word equation in animal cells and the word equation in plant cells. The reactant is the same each time, but the products are different, so the organism named in the question matters.

What the word equation shows

A word equation names the substances that react and the substances made. In anaerobic respiration, glucose is broken down without oxygen, so oxygen must not appear on the left-hand side of either anaerobic equation.

Anaerobic respiration

The release of energy from glucose without using oxygen.

The energy transfer is the reason the process is useful to cells, but energy is not a chemical substance. In a word equation, learn the chemical names first; if energy is shown, it is usually written in brackets after the products.

[DIAGRAM: asset_name: Anaerobic respiration equation routes; asset_slug: b16_anaerobic_respiration__diagram_01; recommended_method: deterministic_drawing; description: Monochrome flow diagram showing glucose branching to animal cells, where the product is lactic acid, and plant cells, where the products are ethanol and carbon dioxide. The diagram also notes that oxygen is not a reactant and energy is released but not written as a substance.]
Diagram

Anaerobic respiration in animals

In animal cells, anaerobic respiration converts glucose into lactic acid.

Plain text

glucose -> lactic acid

This is the equation to use when a question says animals, humans, muscle cells, or animal cells. Carbon dioxide and water are not the products of this animal-cell anaerobic equation.

A common exam slip is to write the aerobic respiration products because the word "respiration" is present. Check the word "anaerobic": if there is no oxygen, the animal-cell product is lactic acid.

Anaerobic respiration in plants

In plant cells, anaerobic respiration produces ethanol and carbon dioxide.

Plain text

glucose -> ethanol + carbon dioxide

This equation is different from the animal-cell equation. Plant cells do not produce lactic acid in the word equation required here. At this level, the same product pattern is often taught using yeast as the example: ethanol is the alcohol product, and carbon dioxide is the gas product.

Use the organism in the question to choose the correct products:

animal cells: lactic acid
plant cells: ethanol and carbon dioxide