Respiration and the Effect of Exercise

• Respiration is a chemical reaction
• Respiration is carried out in all cells continuously
• Respiration releases energy for processes such as movement and keeping warm, and for further chemical reactions
• The word equation for (aerobic) respiration is: glucose + oxygen  carbon dioxide + water
• Organisms have adapted different systems for ensuring all cells receive enough oxygen for respiration
• During exercise, cells require a greater rate of respiration to provide more energy for movement
• Heart rate, breathing rate and breathing volume all increase during exercise to meet the increased demand for the reactants of respiration
• Aerobic respiration uses oxygen and releases more energy than anaerobic respiration
• Anaerobic respiration takes place without oxygen and releases less energy than aerobic respiration
• During intense exercise, if there is not enough oxygen then anaerobic respiration takes place
• Anaerobic respiration in muscle cells causes a build-up of lactic acid
• Anaerobic respiration in muscle cells results in oxygen debt
• Lactic acid is broken down in the liver
• After a long period of intense exercise, muscles become fatigued and cannot contract normally
• The word equation for anaerobic respiration in animal cells is: glucose  lactic acid

Fermentation

• Anaerobic respiration in yeast cells is called fermentation and is used to make bread and alcoholic drinks
• The word equation for anaerobic respiration in yeast cells is: glucose  ethanol + carbon dioxide

Photosynthesis

• Most plants and algae make their own food using a process called photosynthesis
• Almost all life on Earth depends on photosynthetic organisms
• Light provides the energy needed for photosynthesis
• The word equation for photosynthesis is: carbon dioxide + water  glucose + oxygen
• Leaves are the primary site of photosynthesis in plants
• Chloroplasts in plant cells contain a green pigment called chlorophyll which absorbs the energy from sunlight for photosynthesis
• Photosynthesis maintains levels of oxygen in the atmosphere
• Plants carry out aerobic respiration to release energy from glucose
• Plants store glucose as starch
• Iodine is used to test for starch in leaves

Plant Adaptations

• Leaves have a number of adaptations which allow them to carry out photosynthesis effectively
• Plant roots are adapted in order to allow water and minerals to be absorbed
• Water leaves the plant via the stomata on the underside of leaves
• Some plants are non-photosynthetic, which means they cannot carry out photosynthesis
• They tend to be parasitic, often growing in/on/around other plants so they can obtain the food they need
• Examples of parasitic plants include the Indian pipe plant and the beechdrop plant

Biomes

• A biome is an ecosystem with a distinct community of organisms
• A biodome is a self-contained and self-sufficient environment
• Ecosystems recycle resources, including nutrients, oxygen and carbon dioxide

Disciplinary knowledge

• Calculate areas of triangles and rectangles, surface areas and volumes of cubes
• Define the terms precise, accurate and valid, and be able to use these terms in the context of data.
• Decide on a suitable scale for x and y-axis when drawing a graph
• Use an appropriate number of significant figures

Practical skills

• Measure time accurately
• Read a scale accurately
• Observing and measuring biological changes and/or processes, including safe and ethical use of living organisms
• Identify and assess risks to health related to lifestyle habits and the risk of disease.
• Suggest sensible precautions to reduce risk.
• Any anomalous values should be examined to try to identify the cause and, if a product of a poor measurement, ignored.

Variation

• A species is a group of similar organisms that reproduce to make fertile offspring
• A fertile organism is capable of reproduction
• Variation is the difference in characteristics between individual organisms
• There is variation within a population
• Variation can be caused by inherited (genetic) factors, environmental factors or a combination of the two
• DNA is a chemical substance that determines inherited characteristics
• Inherited variation is caused by the fusion of gametes in sexual reproduction and by random mutations in DNA
• Heredity is the process by which genetic information is transmitted from one generation to the next
• Variation between individuals within a species can be continuous or discontinuous
• Continuous variation results in characteristics that can be measured across a range (e.g. height)
• Discontinuous variation results in characteristics that have a limited number of values (e.g. sex)
• Measurements of discontinuous variation result in discrete data
• Frequency tables are used to record characteristics controlled by discontinuous variation
• When graphed, measurements of a feature with continuous variation follow a typical pattern

Artificial and Natural Selection

• Artificial selection is when humans choose plants or animals with particular characteristics to breed
• Artificial selection is continued over many generations until the desired characteristic in the offspring are present
• These characteristics are chosen for appearance or for their usefulness to humans
• Crops and domesticated animals are the result of selective breeding. Examples include pet dogs, crops resistance to disease and cows that make a lot of milk
• Artificial selection can cause inbreeding if closely related individuals are used so that offspring have inherited disease
• Within a community, organisms compete for biotic and abiotic factors to survive and reproduce
• Adaptations are characteristics that allow an organism to survive and reproduce
• Structural adaptations refer to physical features of an organism that allow it to survive and reproduce
• Behavioural adaptations refer to actions of an organism that allow it to survive and reproduce
• Physiological adaptations refer to processes that take place in an organism that allow it to survive and reproduce
• Extremophiles are organisms that are well adapted to live in extreme conditions of temperature, pH, salt or pressure
• Variation between individuals within a species makes some organisms able to compete more successfully
• Natural selection occurs when variation in the population makes some organisms better suited to live and reproduce in a particular environment

Evolution and Extinction

• Charles Darwin proposed the theory of evolution
• Evolution is a change in the inherited characteristics of a population over time caused by natural selection
• Evolution occurs faster in organisms that reproduce rapidly
• Fossils provide evidence for the theory of evolution
• Evolution can cause the formation of a new species
• Changes in the environment may leave individuals within a species, and some entire species, less well adapted to compete successfully and reproduce, which in turn may lead to extinction
• Extinction is when there are no living individuals of a species left in the wild and/or in captivity
• Extinction can be caused by changes to habitats, new predators or competitors or new diseases
• Human activity can accelerate environmental change and cause extinction

Disciplinary knowledge

• Use fractions
• Use percentages
• Calculate percentage increase and decrease
• Construct and interpret frequency tables and results tables
• Considering the best way to present data

Digestion

• The digestive system breaks down molecules in food into soluble substances that can be absorbed and used by cells
• Food passes through the mouth, oesophagus, stomach, small intestine, large intestine, and rectum
• Mechanical digestion is the physical cutting, squashing and churning of food in the digestive system, e.g. by teeth or the stomach
• Chemical digestion is when enzymes and other chemicals are used to speed up reactions in the digestive system
• In the mouth, mechanical and chemical digestion occur
• The salivary glands secrete enzymes which begin the process of chemical digestion
• The oesophagus moves food into the stomach. Rings of smooth muscle squeeze food in a mechanical process called peristalsis.
• In the stomach, mechanical and chemical digestion occur
• The stomach contains acid to kill micro-organisms in food
• Bile is made in the liver and stored in the gall bladder
• Bile is alkaline and neutralises the acid in the stomach
• Bile makes fat form smaller droplets
• Chemical digestion takes place in the small intestine. Small, soluble molecules move into the bloodstream by diffusion
• The small intestine is well adapted to its function because it has many villi which increase the surface area to increase diffusion of nutrient molecules into the blood. It is also very long which also increases the surface area. It also has a good blood supply which allows nutrient molecules to be absorbed into the blood
• Water is absorbed into the bloodstream from the large intestine
• Undigested food leaves the digestive system via the anus during a process called egestion
• The digestive system contains many bacteria. These bacteria help with the digestion of certain substances, reduce the change of harmful bacteria causing disease, and produce some vitamins that humans need, e.g. vitamin B and K

Digestive Enzymes

• Enzymes speeds up chemical reactions in the body
• Digestive enzymes break down large nutrient molecules into smaller molecules that can be absorbed into blood and used by cells
• Carbohydrases, such as amylase, break down carbohydrates into simple sugars
• Lipases break down lipids in glycerol and fatty acids
• Proteases break down proteins in to amino acids
• The lock and key theory models how enzymes work by having an active site that is a specific shape to the substrate it joins to

Food Tests

• Iodine solution changes colour from brown to black in the presence of starch
• Benedict’s reagent changes colour from blue to orange/red when heated in the presence of simple sugars such as glucose
• Biuret reagent changes colour from blue to purple in the presence of protein

A Balanced Diet

• The contents of a healthy human diet include carbohydrates, lipids (fats and oils), protein, vitamins, minerals, dietary fibre and water
• A balanced diet includes all the nutrients our body needs in the right quantities
• Malnourishment occurs when a person does not have a balanced diet
• Carbohydrates are important to provide energy. Carbohydrates are found in foods such as bread, potatoes, rice and pasta
• Lipids are important for providing energy and insulation. Lipids are found in foods such as nuts, dairy products, meat, oils and sweets
• Proteins are important for growth and repair of cells and tissues. Proteins are found in foods such as eggs, pulses, fish, meat, nuts and dairy products
• Vitamins and minerals are important because they all have roles in essential processes in the body. Vitamins and minerals are found in high quantities in fruit and vegetables, but are provided by all parts of the diet
• Calcium is an example of a mineral used in making bones and teeth
• Fibre is important for adding bulk to food and helping it pass through the digestive system. Fibre is found in foods such as fruit, vegetables and wholegrain cereals
• Water allows for transport of substances around the body and for chemical reactions to occur in cells
• Imbalances in the diet can result in health consequences, including obesity, starvation and deficiency diseases
• An example of a deficiency disease is kwashiorkor, caused by a lack of protein

Plant Nutrition

• Plants require minerals for healthy growth
• Plants need nitrates to make proteins (for growth). Plants get nitrates from the soil, through their roots
• Plants need magnesium to make chlorophyll. Plants get the magnesium they need from the soil via their roots
• Plants can be damaged by a range of deficiency conditions. A deficiency in magnesium affects photosynthesis

Disciplinary knowledge

• Use of appropriate techniques and qualitative reagents to identify biological molecules and processes in more complex and problem-solving contexts including continuous sampling in an investigation
• Critique and evaluate models, including:
• Make predictions or calculate quantities based on the model or show its limitations.
• Give examples of ways in which a model can be tested by observation or experiment.
• Evaluate the strengths and limitations of a model
• Identify names and uses of basic lab equipment and apparatus
• Draw a line of best fit

Practical skills

• Safe use of heating devices and techniques, including Bunsen burner, electric heater and water bath
• Measure pH
• Describe representative sampling techniques
• Apply representative sampling techniques and explain why it is appropriate
• Identify and assess risks to health related to lifestyle habits and the risk of disease.
• Suggest sensible precautions to reduce risk.
• Safe use of equipment to separate mixtures using chromatography
• Suggest a hypothesis to explain given observations or data.
• Explain why a certain hypothesis was chosen, with reference to scientific theories and explanations

Eukaryotic and Prokaryotic Cells

• Eukaryotic cells have membrane-bound organelles and have genetic material contained in the nucleus
• An organelle is a part of a cell that carries out a specific function
• Plant and animal cells are examples of eukaryotic cells
• Eukaryotic cells are typically between 10-100 μm in size
• 1 μm is equal to 1 x 10-6 m
• All eukaryotic cells have a nucleus, mitochondria, ribosomes, cytoplasm and a cell membrane. Plant cells also have a cell wall, vacuole and chloroplasts
• Mitochondria are the site of aerobic respiration which releases energy for cellular processes
• Ribosomes are the site of protein synthesis
• Chloroplasts contain chlorophyll to allow for photosynthesis
• The cell membrane controls the movement of substances in and out of a cell
• The cytoplasm is the site of chemical reactions within a cell
• The cell wall provides support and rigidity to plant cells and is made of cellulose
• The vacuole contains cell sap and provides rigidity to plant cells
• Prokaryotic cells do not contain membrane-bound organelles
• Prokaryotic cells are much smaller than eukaryotic cells. They are typically between 1-10 μm in size.
• Prokaryotic cells are approximately 10 orders of magnitude smaller than eukaryotic cells
• Prokaryotic cells contain genetic material in small rings called plasmids, or in larger loops
• Prokaryotic ribosomes are smaller than eukaryotic ribosomes

Aseptic Technique

• Petri dishes are used to produce cultures of bacteria and other micro-organisms
• Cultured bacteria are grown on a nutrient medium in controlled conditions
• Aseptic techniques must be used to prepare cultures to prevent contamination of the culture and the growth of harmful bacteria
• Petri dishes, inoculating loops and culture media must be sterilised before use. A flame can be used to sterilise equipment
• An inoculating loop is a piece of equipment used to transfer bacteria to the petri dish
• The lid of a Petri dish should be partially secured with tape to ensure bacteria cannot escape but conditions remain aerobic
• The Petri dish must be stored upside down to prevent condensation affecting bacterial growth
• In school laboratories, cultures should generally be incubated at 25 °C to prevent the growth of harmful bacteria
• A cotton wool swab can be used to transfer a sample to a Petri dish to investigate bacterial growth
• Bacteria on a Petri dish divide rapidly whilst the nutrient supply is rich. Every time the bacteria reproduce, the number doubles. The total number of bacteria can be calculated using the following formula: Final number of bacteria = Initial number of bacteria x 2number of divisions

Microscopes

• Microscopy is the field of using microscopes to view samples that cannot be seen with the naked eye
• Microscopy has developed over time
• Light microscopes allow us to see the largest organelles, including the nucleus, cell membrane, cell wall and cytoplasm. A stain is often used to make the organelles clearer
• The parts of a light microscope include the eyepiece lens, objective lenses, stage, coarse focusing wheel, fine focusing wheel, light/mirror
• A sample used with a light microscope must be very thin to allow light to pass through
• The specimen to be viewed under a microscope is placed on the stage and secured with stage clips
• The eyepiece lens and objective lens are used to increase the size of the image
• The coarse focusing wheel is used to move the stage and get the cells into frame
• The fine focusing wheel is used to sharpen an image
• The total magnification of a microscope can be calculated using the following equation: Total magnification = Objective lens x eyepiece lens
• Electron microscopes have a greater magnification and resolution than light microscopes. They are much more expensive than light microscopes
• Magnification is the number of times larger an image is than the object
• Resolution is the ability to distinguish between two points
• Electron microscopes allow are to see more organelles and study cells in greater detail
• Magnification can be calculated using the following equation: Magnification= Size of imageSize of object
• A scale bar can be used to calculate the magnification of an irregular object
• Magnification does not have a unit because it is a ratio

Diffusion

• Diffusion is the spreading out of particles, of a gas or liquid, resulting in net movement from an area of high concentration to low concentration
• Diffusion of some substances can happen through the cell membrane
• In gas exchange, oxygen and carbon dioxide diffuse between the alveoli and the blood
• Urea is a waste product made by cells that needs to be excreted by the kidneys. Urea diffuses from cells into blood
• The rate of diffusion is increased by: an increase in temperature, an increases in the difference in concentrations (concentration gradient) and by a greater surface area
• Unicellular organisms have a relatively high surface area to volume ratio allowing for sufficient transport of all required substances
• Large, multicellular organisms have adaptations to increases the surface area to volume ratio to allow for efficient exchange of substances
• The cell membrane is very thin so provides a short diffusion path
• In plants, the structure of leaves and roots increases the surface area for diffusion
• The lungs of mammals, birds and reptiles are well ventilated, have a large surface area and an efficient blood supply to maximise the rate of diffusion
• The gills of fish have a large surface area and efficient blood supply to maintain a high concentration gradient for diffusion

Osmosis

• Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Only water can move by osmosis
• A partially permeable membrane is a membrane that lets particular substances pass through it, either into or out of the cell
• A hypertonic solution is one in which the external solution has a higher concentration of solute than the cell. Water always moves out of a cell that is placed in a hypertonic solution, causing the cell to shrivel or become flaccid
• Tissue placed in hypertonic solutions decreases in mass
• A hypotonic solution is one in which the external solution has a lower concentration of solute than the cell. Water always moves into a cell that is placed in a hypotonic solution, causing the cell to swell or become turgid
• Tissue placed in hypotonic solutions increases in mass
• An isotonic solution is one in which the external solution has the same concentration of solute as the cell. Water will not move in or out of cells placed in an isotonic solution so their size will stay constant
• Guard cells open and close due to the movement of water by osmosis
• The mass of plant tissue can be measured before and after being placed in a solution of known concentration to calculate the percentage change in mass due to osmosis

Active Transport

• Active transport is the movement of substances from a more dilute solution to a more concentrated solution, requiring energy from respiration
• Active transport works against the concentration gradient
• Some substances are moved into a cell by both diffusion and active transport
• Active transport is used in the small intestine/gut to transport glucose into the blood for transport to cells for respiration
• Active transport is used in root hair cells to absorb mineral ions from the soil that are essential for plant growth
• Plants growing in waterlogged soils cannot absorb mineral ions because the cells do not have access to oxygen for respiration

Cell Growth and Division

• Both eukaryotic and prokaryotic cells undergo cell division
• Cells increase in number by dividing into two
• The eukaryotic cell cycle contains a growth phase where the cell grows to double sub-cellular structures (such ribosomes and cell membrane) and DNA, then the cell splits into two during mitosis
• The cell cycle of different cells lasts different lengths of time
• A microscope can be used to observe cells in different stages of the cell cycle
• The length of time in a certain stage of the cell cycle can be calculated using the following formula: observed number of cells at that stagetotal number of cells observed x total length of time of cell cycle
• The mass of DNA in a cell doubles during the growth phase of the cell cycle
• The mass of DNA in a cell can be measured in picograms
• 1 picogram = 1 x 109 g
• During mitosis DNA (arranged into chromosomes) is pulled to separate ends of the cell ready for division
• The final part of the cell cycle is when the cell membrane splits to produce two identical cells
• Mitosis is used by eukaryotic organisms for growth and repair
• Mitosis is used by eukaryotic organisms that asexually reproduce
• Mitosis does not occur in prokaryotic cells because they do not possess a nucleus
• Checkpoints in the cell cycle control the rate of cell division
• Cancer is caused by uncontrolled cell division
• A tumour is a mass of cells caused by uncontrolled cell division
• Benign tumours are a mass of cells contained in one area
• Malignant tumours are formed of cancer cells that invade other tissues and spread around the body where they form secondary tumours
• A risk factor is a gene or lifestyle choice that can increase the likelihood of a person developing a disease
• Lifestyle risk factors for cancer include poor diet, lack of exercise, smoking, UV exposure
• Genetic risk factors for cancer include gene mutations

Stem Cells

• Specialised cells arise from stem cells
• Stem cells are cells that are capable of differentiating into other types of cell
• When a cell differentiates, it acquires specific structures needed for that cell type
• Most animal cells differentiate at an early stage of development
• Embryonic stem cells can differentiate into all human cell types
• Adult bone marrow contains stem cells that can differentiate into different types of blood cell
• Embryonic stem cells can be used to study and treat diseases. There are religious and ethical objections to using embryonic stem cells in scientific research
• Plants contain meristem tissue at the tips of shoots and roots that retains the ability to differentiate throughout a plant’s life

Disciplinary Knowledge

• Change the subject of an equation
• Use percentages
• calculate percentage increase and decrease
• Identify in a given context:
• the independent variable as the one that is changed or selected by the investigator
• the dependent variable that is measured for each change in the independent variable
• Outline a simple ethical argument about the rights and wrongs of a new development, discovery or technology
• Explain that there are hazards associated with science-based technologies which have to be considered alongside the benefits
• Suggest a hypothesis to explain given observations or data
• Explain why a certain hypothesis was chosen, with reference to scientific theories and explanations
• Identify and assess risks to health related to lifestyle habits and the risk of disease
• Suggest sensible precautions to reduce risk

Practical Skills

• Application of aseptic technique
• Prepare a slide with cells for viewing under the light microscope
• Obtain a clear image using a light microscope
• Measure mass accurately