Bioenergetics GCSE

Cellular respiration

Process that releases energy by breaking down glucose and other food molecules

Exothermic reaction

A reaction that releases energy to its surroundings, usually in the form of heat

Aerobic respiration

Cell respiration which happens in the presence of oxygen in the mitochondria of the cell

Word equation for aerobic respiration

Glucose + oxygen -> carbon dioxide + water (+energy)

Balanced chemical equation for aerobic respiration

C6H12O6 + 6O2 -> 6CO2 + 6H2O

Anaerobic respiration

Cell respiration which happens in the absence of oxygen

Word equation for anaerobic respiration

Glucose -> lactic acid (+energy)

Lactic acid

A toxic waste product that is produced during anaerobic respiration in humans and can cause muscle fatigue

Incomplete oxidation

Occurs during anaerobic respiration causing a build up of lactic acid in the muscles

Fermentation

Anaerobic respiration in plant and yeast cells which produces ethanol and carbon dioxide

Word equation for fermentation

Glucose -> carbon dioxide + ethanol (+energy)

Uses of fermentation

The manufacture of bread and alcoholic drinks

Liver

Receives blood from the muscles with lactic acid and converts the lactic acid back into glucose

Oxygen debt

The amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid

Effect of exercise

Increased heart rate, breathing rate and breath volume to supply the muscles with more oxygen

Organisms need energy for

Movement, keeping warm and chemical reactions to make larger molecules

Glucose (C6H12O6)

The main reactant of respiration that is obtained from the digestion of carbohydrates

Oxygen (O2)

A molecule that is essential for the complete oxidation of glucose in aerobic respiration

Carbon dioxide (CO2)

A waste product of respiration that is removed from cells and the body via gas exchange

Water (H2O)

A byproduct of respiration that is either used or removed from the body typically during exhalation or urination

Metabolism

The sum of all the reactions in a cell or the body

Metabolism includes

The synthesis of new molecules, the breakdown of existing molecules and the process of respiration

Energy transferred by cellular respiration

Is used by organisms for the continual enzyme-controlled processes of metabolism

Enzymes and metabolism

Enzymes regulate most cellular reactions and are essential for the synthesis and breakdown of molecules

Conversion of glucose to complex carbohydrates

Glucose can be converted into starch, glycogen and cellulose

Formation of lipid molecules

One molecule of glycerol joins with three fatty acids

Amino acid production

Glucose and nitrate ions form amino acids which are used to make proteins

Protein synthesis

Amino acids join together in specific arrangements to form proteins

Urea excretion

Excess proteins are broken down to form urea for excretion

Digestion

Requires energy from respiration to break down large insoluble molecules into smaller soluble molecules

Carbohydrates

Provide energy for chemical reactions and can break down into sugars

Proteins

The building blocks of cells and tissues that can break down into amino acids

Lipids

An energy store of fats and oils that can break down into glycerol and fatty acids

Photosynthesis

A process where plants and algae synthesise glucose from carbon dioxide and water, using light energy from the sun

Photosynthesis word equation

Carbon dioxide + water (+light energy) -> glucose + oxygen

Balanced equation for photosynthesis

6CO2 + 6H2O -> C6H12O6 + 6O2

Glucose (C6H12O6)

The main chemical product of photosynthesis that has many different uses in a plant, including respiration

Oxygen (O2)

A waste product of photosynthesis that leaves the plant through the stomata of the leaves or can be used for respiration

Carbon dioxide (CO2)

A reactant needed for photosynthesis to synthesise glucose, this gas enters the plant via gas exchange through the stomata of the leaves

Water (H2O)

A reactant needed for photosynthesis to take place, water is absorbed by the roots and is transported by the xylem to reach the leaves where photosynthesis occurs

Endothermic reaction

A chemical reaction where energy is taken in from the surrounding environment

Chloroplast

An organelle found in plant and algae cells where photosynthesis occurs

Chlorophyll

A green pigment in plants that absorbs light energy used to carry out photosynthesis

Temperature effect

Photosynthesis rate increases to an optimum and then decreases due to denaturing enzymes

Light intensity effect

Photosynthesis rate increases as more energy is available, up to a certain point

Carbon dioxide concentration effect

Photosynthesis rate increases as more carbon is available to synthesise glucose, up to a certain point

Photosynthetic rate

The rate at which plants take in carbon dioxide, water and the energy from sunlight to produce glucose

Limiting factor

An environmental factor that prevents photosynthetic rate from increasing

Insoluble starch

A complex carbohydrate made from the products of photosynthesis and used for storage, stored in the leaves if photosynthesis can produce sufficient quantities of glucose

Testing leaves for starch

Plant leaves can be tested for the presence of starch using iodine solution, after the leaf has been intensely heated and submerged in ethanol

Fats and oil

Lipids which can be made from the products of photosynthesis for storage

Cellulose

Carbohydrate component of plant cell walls which can be made from the products of photosynthesis

Amino acids

Building blocks of protein which along with nitrates can be made from the products of photosynthesis

Photosynthetic rate

The rate at which plants take in carbon dioxide, water and the energy from sunlight to produce glucose and oxygen

Light intensity

A factor that typically increases the rate of photosynthesis

Distance from light source

The independent variable or factor that is changed in this experiment to investigate photosynthesis

LED light source

Is used as it releases less heat compared with other light bulbs

Temperature

A variable that should be controlled in this experiment to ensure the results are valid

Sodium hydrogen carbonate

Added to the water to supply the pondweed with a controlled source of carbon dioxide

Pondweed

A species of aquatic plant such as Cabomba or Elodea

Acclimatise

Allow the pondweed time to settle during each test before recording data to ensure results are valid

Bubbles of gas

The pondweed should release oxygen bubbles that can be counted as a measure of photosynthetic rate

Number of oxygen bubbles

The dependent variable or factor that is measured in this experiment to investigate photosynthesis

Mean average

The total sum of the data values divided by the number of times the data was recorded

Volume of oxygen gas

A more accurate experiment would be to collect the oxygen in an inverted measuring cylinder and record the volume

Expected results

As distance from the light source doubles, the number of bubbles per minute should decrease by a factor of four

Inverse-square law

Light intensity is inversely proportional to the square of the distance from a light source

Inversely proportional relationship

As the distance of light from a plant increases, the light intensity decreases

Water bath

A container of water heated to a given temperature for control purposes

Examples of other control variables

To ensure the results are valid the volume, concentration, external light and pondweed variety should be controlled