Investigating Living Cells
State 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 cells
Most 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 them
b. flat and not folded- to let us see the cells clearly
c. moist - to stop the cells drying up
d. 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.
Structure / FunctionNucleus / Controls cell activities
Cytoplasm / Site of reactions
Cell membrane / Controls the entry and exit of materials into and out of the cell
Large vacuole / Contains cell sap
Chloroplast / Site of photosynthesis
Cell wall / Rigid to give the cell shape
Similarities Differences
All cells have: In addition plant cells have:
1. nucleus 1. vacuole
2. cell membrane 2. chloroplast
3. cytoplasm 3. cell wall
Investigating Diffusion
State 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 an
area 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.
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 cellGlucose / High / Low
Carbon dioxide / Low / High
Oxygen / High / Low
Waste / 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.
Investigating Cell Division
The 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 organism
and 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.
Identify the correct sequence of stages of mitosis
Investigating Enzymes
The 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’
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 à 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
amylase
starch à 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 phosphorylase
Glucose – 1 – phosphate à starch
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 too
high 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
Investigating Aerobic Respiration
State 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 Eats
ii Plant cells can Make their own food by a process called PHOTOSYNTHESIS
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 equation
GLUCOSE + OXYGEN à ENERGY + CARBON DIOXIDE +WATER
raw 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.
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