Investigating Living CellsState that cells are the basic units of living things

All living things (plants and animals) are made up of at least one cell.Cells are called the basic unit of living things, in the same way that bricks are the basic unit of a building like this school.Microscopes and cellsMost cells are very small, and can only be seen properly by looking at them under a microscope.When looking at cells under a microscope they must be: a. thin – to let the light pass through themb. flat and not folded- to let us see the cells clearlyc. moist - to stop the cells drying upd. clear of air bubbles - these can spoil the clear view of the

cells

Explain the purpose of staining animal and plant cells

Stains are used to show up internal structures which would not otherwise be seen.

Unstained specimen specimen stained with iodine solution

Describe the structural similarities of and differences between animal and plant cells

Cells can be a variety of different shapes and sizes, but they all have structures in common. When we look closely at plant and animal cells, we can also notice that the plant cells have structures that are not found in animal cells – plant cells are different from animal cells.

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Structure FunctionNucleus Controls cell activitiesCytoplasm Site of reactionsCell membrane

Controls the entry and exit of materials into and out of the cell

Large vacuole Contains cell sapChloroplast Site of photosynthesisCell wall Rigid to give the cell shape

Similarities Differences

All cells have: In addition plant cells have:1. nucleus 1. vacuole2. cell membrane 2. chloroplast3. cytoplasm 3. cell wall

Investigating DiffusionState that a substance can diffuse from a high concentration to a low one

Any substances that need to move into or out of cells must move through the cell membrane. To do this the substance must be dissolved in a liquid like water.The process that allows substances to move into and out of cells is called DIFFUSION.Diffusion is the movement of a substance from an area of high concentration to anarea of low concentration.

the cell membrane controls the passage of substances into and out of the cell

Cell membranes control what can enter or leave the cell because they have tiny pores in them that only allow small substances to pass through by diffusion.Explain the importance of diffusion to organisms

Cell membranes have tiny pores in them that allow only small substances to pass through them by diffusion, as long as the small substances are soluble (dissolved in a liquid).

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Many substances need to be transported into cells – these are needed to allow the cell to function properly.Many substances need to be transported out of cells – these include waste products that would poison the cells.

Give examples of substances which enter and leave the cell by diffusion, e.g. dissolved food, oxygen, carbon dioxide and water

Substance Concentration OUTSIDE cell Concentration INSIDE cell

Glucose High LowCarbon dioxide Low HighOxygen High LowWaste Low High

cell

Diffusion is a very important process for all living cells because it ensures that all the substances a cell needs move into the cell, and all the ones the cell does not need move out of the cell. Remember . . . substances always move from a high concentration to a low concentration.

Identify osmosis as a ‘special case’ of the diffusion of water

Water is a very important substance to all living cells, water will move into cells if they have too little and move out of cells if they have too much. Water moves in or out of cells by a special type of diffusion called osmosis. Osmosis only ever involves the movement of water.Osmosis is a special case of diffusion that only involves water moving from an area of high water concentration to a region of low water concentration. Explain osmosis in terms of a selectively permeable membrane and of a concentration gradient

If substances can pass through a membrane we say that the membrane is permeable. Since cell membranes can choose or select which substances can pass through them (small ones only), we say that the membrane is selectively permeable.The bigger the concentration gradient between the inside and outside of the cell the quicker the water will move by osmosis. Osmosis is the movement of water down a concentration gradient through a selectively permeable membrane.

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Useful substances

Waste substances

oxygen

glucose

Carbon dioxide

waste

Explain observed osmotic effects in plants and in animal cells in terms of the concentration of water in the solutions involved

There are three different situations a cell can be in when investigating osmosis.1 The water concentration outside the cell is the same as inside.2 The water concentration outside the cell is higher than inside.3 The water concentration outside the cell is lower than outside.

In the first situation, water moves in and out at the same rate and the cell stays the same – it neither gains nor loses water.In situation 2 the water moves from a high concentration outside the cell to a lower concentration inside.In situation 3 the water moves from a high concentration inside the cell to a lower concentration outside the cell.

Animal cells e.g. red blood cellsCells placed in pure/distilled waterWater enters the cell, the cell swells and bursts

Cells placed in a solution of equal water concentration

There is no net movement of water so the cell

stays the samecells placed in a strong salt/sucrose solution(low water concentration)Water moves out of the cell. The cell shrinks

Plant cells e.g. onion cellsCell placed in pure/distilled water

Water moves inCell is turgid

Cell placed in a solution of equal water concentration There is no net movement of water so the cell is unchanged

cell placed in strong sucrose/salt solution . Water moves out of the cell by osmosis and the cell is plasmolysed

Turgid cells Plasmolysed cellsExternal solution

Pure water Strong sucrose

Appearance of Pushed up against the Pulled away from the cell

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Cell membrane cell wall wallShape of vacuole

Full Shrunk

Appearance of Cell wall

Stretched slightly Normal

Plant cells do not burst when placed in distilled water as the cell wall stops them from doing so.

Investigating Cell DivisionThe nucleus of every cell contains all the information that is needed for that cell to carry out all of its necessary functions. This information is present in thread-like structures called chromosomes. Chromosomes are made up of genes. Chromosomes are only seen using a very powerful microscope because they are very small.

State that cell division is a means of increasing the number of cells in an organismand occurs when a cell divides (splits) to form two new cells.

Cells divide when there is a need to increase the number of cells in the organism i.e. when:1 The organism is growing (remember we all began life as a single cell).2 Bone cells divide to repair a break (or a fracture).3 Skin cells divide to heal a wound (or a cut).4 A zygote (fertilised egg cell) divides to form an embryo. This is called

development.

State that the nucleus of the cell controls cell activities including division

State that each of the two cells produced by cell division has a complete set of chromosomes and the same information

Two cells are made when a cell divides.These new cells are exactly the same as each other and the cell that they came from (the mother cell).They are identical to each other because they have the same information – the same number and type of chromosome in their nucleus.The chromosomes in the nucleus of the mother cell are copied before division so that each new cell has a full set.

Describe the stages of mitosis

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Stage 1 each chromosome in the nucleus of the mother cell makes a copy of itself.Stage 2 Chromosomes are now made up of 2 chromatids joined at a point called the centromere. The membrane around the

nucleus disappears.Stage 3 the chromosomes (made up of

2 chromatids) line up along the equator of the cell

Stage 4 The 2 chromatids of each chromosome are pulled apart (separated) by long, thin structures called spindle fibres.The chromatids of each chromosome are pulled to opposite ends of the cell (the poles). The chromatids are now called chromosomes again.

Stage5 A membrane forms around each of the two groups of chromosomes. The cell now has 2 identical nuclei. The nucleus has now divided. The mother cell starts to be pulled in around its middle.Stage6 The cytoplasm divides into 2 identical halves. The cytoplasm has now divided. The original mother cell has now divided into two identical daughter Cells. Mitosis is now complete.

Explain why it is important that the chromosome complement of daughter cells in multicellular organisms is maintained

Cells made by mitosis are identical to each other and the mother cell they came from.They have the same chromosome complement – same type and number of chromosomes.This is important as it allows new cells to carry out an identical job as the mother cell.

Identify the correct sequence of stages of mitosis

Investigating EnzymesThe cytoplasm is the site of chemical reactions.

Explain why enzymes are required for the functioning of living cells

Enzymes are proteins that speed up the rate of chemical reactions. Without enzymes, chemical reactions would take place too slowly to allow life to continue.

Explain the meaning of the term ‘catalyst’

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Catalysts are special chemicals that speed up the rate of a chemical reaction but remain unchanged themselves. Catalysts can be used again.

Enzymes are called biological catalysts since they are produced by living cells.

Hydrogen peroxide water + oxygen

All living cells contain the enzyme catalase which speeds up the breakdown of hydrogen peroxide.

There are 2 types of chemical reaction: synthesis (build up)degradation (break down)

Give an example of an enzyme involved in the chemical breakdown of a substance

amylasestarch maltose

Give an example of an enzyme involved in synthesis

Green plants make glucose by photosynthesis. Extra glucose is stored as starch.The synthesis enzyme that builds up glucose into starch is called phosphorylase. Phosphorylase is found in large quantities in potato tubers.

Potato phosphorylaseGlucose – 1 – phosphate starch

Explain the term ‘specific’ as applied to enzymes and their substrates

All enzymes are specific because they work on only one type of substrate.

Enzyme Type of reaction catalysed

Substrate Product(s)

Amylase Degradation Starch MaltoseCatalase Degradation Hydrogen peroxide Water + oxygenPhosphoryla Synthesis Glucose-1-phosphate Starch

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Enzymes recognise their substrates by their shapes.

Enzymes are like keys because they: match

exactly into the shape of one substrate this is the

LOCK and KEY theory

State that enzymes are proteins

Describe the effect of temperature on enzyme activity

Enzymes work best at certain temperatures, they work slower if the temperature is too cold. If the temperature is too hot, the enzyme stops working altogether, this change cannot be reversed. The enzyme changes shape and stop working and this change is permanent. When this occurs (temperatures above 50 C) we say that enzymes are denatured.

Describe the effect of a range of pH on the activity of pepsin and catalase

Like temperature, pH affects how fast an enzyme works. The activity of an enzyme is affected by how acid or alkali it is, this is called the pH of an enzyme. Most enzymes work best at neutral pH of number 7. The enzyme pepsin works in a pH range of pH 1 to pH 5 but works best at pH 3. If the pH is toohigh or too low the enzyme does not work as fast as it could do. The enzyme catalase is active in the pH range of pH 6 to pH 12 but is most active at pH 9

Explain the term optimum as applied to the range of conditions in which enzymes operate

The conditions that allow an enzyme to work best are called optimum conditions.The temperature an enzyme works best at is called its optimum temperature.The optimum temperature for human enzymes is 37oC. The optimum temperature for plant enzymes is between 20oC and 25oCThe pH an enzyme works best at is called its optimum pH.The optimum pH for: catalase is pH 9; pepsin is pH 3

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Investigating Aerobic RespirationState three reasons why living cells need energy

All cells need energy to carry out important functions like: a making more of themselves (Cell division)b increasing their size (Growth)c building up or breaking down substances in

the cell (Chemical reactions)d allowing the cell to change position (Movement)e keeping the temperature of the cell constant

(Heat production)

All cells get their energy from food and how they get their food depends on the type of cell:i Animal cells get their food when the animal Eatsii Plant cells can Make their own food by a process called PHOTOSYNTHESIS

State that fats and oils contain more chemical energy per gram than carbohydrates or proteins

The energy in our food is used in respiration to provide our cells with energy in a form that they can use. Fats contain twice as much energy per gram as carbohydrates or protein.

State that cells need oxygen to release energy from food during aerobic respiration

Living cells use the gas Oxygen when they carry out Aerobic respiration.

Describe aerobic respiration in terms of a word equation9

Carbohydrate 19KJ/g

Protein 19KJ/g

Fat 38KJ/g

GLUCOSE + OXYGEN ENERGY + CARBON DIOXIDE +WATERraw materials useful product waste products

State that carbon dioxide is given off by cells during tissue respiration and is derived from food

All living cells produce the gas carbon dioxide when they carry out aerobic respiration.The carbon dioxide comes from the food. Remember glucose contains carbon, hydrogen and oxygen.

State that heat energy may be released from cells during respiration

Some of this energy is released as heat. This is important to warm blooded animals who need to maintain their body temperature at a constant level.

Explain the importance of energy released from food during respiration to the metabolism of cells

All the chemical reactions that occur in the cytoplasm of a cell are, together known as the metabolism of the cell. Every one of these reactions is controlled by an enzyme.There are 2 different types of chemical reaction that make up the metabolism of a cell: Synthesis and DegradationBuild up reactions usually use energy and breakdown reactions usually release energy.Respiration is important because it provides the energy to allow all the other reactions in the cell to occur.

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