Year 9

Biology GCSERevision Guide

Term 1

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Contents

1. Animal and Plant Cells (Page 3)2. Differentiation of Cells / Specialised Cells (Page 4)3. Organisation within organisms (Page 5)4. Diffusion (Page 7)5. Osmosis (Page 8)6. Active Transport (Page 9)7. Enzymes (Page 11)8. Factors affecting enzymes (Page 13/ 14)

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Animal and Plant Cells

All animals and plants are made of cells. Animal cells and plant cells have features in common, such as a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cell wall, and often have chloroplasts and a permanent vacuole. Note that cells may be specialised to carry out a particular function.

Function of cells which animal and plant cells have in common

part function

nucleus contains genetic material, which controls the activities of the cell

cytoplasm most chemical processes take place here, controlled by enzymes

cell membrane

controls the movement of substances into and out of the cell

mitochondria most energy is released by respiration here

ribosomes protein synthesis happens here

Plant cells also have extra parts:

part function

cell wall strengthens the cell

chloroplasts contain chlorophyll, which absorbs light energy for photosynthesis

permanent vacuole

filled with cell sap to help keep the cell turgid

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Specialised Cells

Cells may be specialised for a particular function. Their structure will allow them to carry this function out. Here are some examples of cells and how they are specialised to carry out their function (job).

Type of animal cell Function Special features

Red blood cells To carry oxygen Large surface area

Contains haemoglobin

White Blood Cell To destroy pathogens (germs) Can engulf cells

Can produce antibodies

Nerve cells To carry nerve impulses (electrical signals) to different parts of the body

Long to carry signals all over the body

Synapses at each end for control

Fatty sheaf to help carry signals faster

Female reproductive cell (egg cell)

To join with male cell, and then to provide food for the new cell that's been formed

Large so contains lots of cytoplasm (nutrients for the growing embryo)

23 Chromosomes in the nucleus (half of a normal cell)

Male reproductive cell (sperm cell)

To reach female cell, and join with it

Long tail for swimming

Head contains 23 chromosomes in the nucleus (half of a normal cell)

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Organisation in organisms

In order of increasing complexity, multicellular organisms consist of:

organelles → cells → tissues → organs → organ systems

Structure Description

Organelle Cell structure that is specialised to carry out a particular function or job

Cell Basic structural and functional unit of a living organism

Tissue Group of cells with similar structures, working together to perform a shared function

Organ Structure made up of a group of tissues, working together to perform specific functions

Organ system

Group of organs with related functions, working together to perform body functions

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Questions to test your knowledge so far:

Name the part of your cell that controls what enters and exits

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Name the part of the plant cell that carries out photosynthesis

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What type of cell is this? What features help you to work this out?

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What features make a sperm cell specialised for its job?

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What is the function of the red blood cell?

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What three features do all cells have?

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_________________________

_________________________

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Diffusion

Diffusion occurs when particles spread.

They move from a region where they are in high concentration to a region where they are in low concentration.

Diffusion happens when the particles are free to move. Diffusion can happen in liquids and in gases. Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration. This is how the smell of cooking travels around the house from the kitchen, for example

Remember, particles continue to move from a high to a low concentration while there is a concentration gradient until they reach equilibrium (the concentrations are equal).

Key Points to remember;

Diffusion doesn’t need any energy Diffusion doesn’t need a membrane Diffusion is the movement of particles DOWN a concentration gradient (from

high concentration to low concentration).

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Osmosis

Water can move across cell membranes because of osmosis. For osmosis to happen you need:

two solutions with different concentrations a partially permeable membrane to separate them

Partially permeable membranes let some substances pass through them, but not others.

Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane.

Eventually the level on the more concentrated side of the membrane rises, while the one on the less concentrated side falls. When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions.

Key Points to remember;

Osmosis doesn’t need any energy Osmosis needs a partially permeable membrane Osmosis is the movement of WATER only Osmosis is the movement of water DOWN a concentration gradient (from high

concentration to low concentration).

Active Transport

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Active transport is the process by which dissolved molecules move across a cell membrane from a lower to a higher concentration. In active transport, particles move against the concentration gradient - and therefore require energy from the cell.

Sometimes dissolved molecules are at a higher concentration inside the cell than outside, but, because the organism needs these molecules, they still have to be absorbed. Carrier proteins pick up specific molecules and take them through the cell membrane against the concentration gradient

Key Points to remember;

Active Transport needs energy Active Transport needs a partially permeable membrane Active Transport is the movement of water UP a concentration gradient (from

low concentration to high concentration).

Questions to test your knowledge so far:

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Which type of movement doesn’t need a membrane?

______________________________

Which type of movement needs energy?

______________________________

What type of movement will happen in this image. Use your knowledge to explain why you know this.

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What does osmosis and active transport have in common?

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What does osmosis and diffusion have in common?

_________________________________________________________________________________________________________________________________________________________________________________________________________

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Enzymes

Enzymes are made of proteins and are used to speed up reaction inside our bodies. They are called biological catalysts. Enzymes have an active site which is a specific shape. It is the shape of the enzymes active site that allows it to do its job and makes it specific to its substrate (the thing that it breaks down).

There are optimum temperatures and pH values that enzymes work best at. Enzymes are usually denatured above about 45ºC.

Denatured: this means that the shape of the protein changes and it can no-longer work.

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Lock and Key Model

Enzymes are specific. Only molecules with the correct shape can fit into the enzyme. Just like only one key can open a lock, only one type of enzyme can speed up a specific reaction. This is called the lock and key model.

There are three main stages shows in the diagram below;

1. The substrate is the same shape and size as the active site on the enzyme. 2. The substrate joins to the active site and forms an enzyme-substrate

complex.3. The enzyme can then either break the substrate into products or jois the

substrates together into a new product which get released form the active site.

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Factors affecting Enzymes

Enzymes work best at their optimum temperature. This is why it’s important to keep our body temperature at a constant 37°C.

A common error in exams is to write that enzymes are killed at high temperatures. Since enzymes are not living things, they cannot be killed.

Temperature and enzymes

As the temperature increases, so does the rate of chemical reaction. This is because heat energy causes more collisions, with more energy, between the enzyme molecules and other molecules. However, if the temperature gets too high, the enzyme is denatured and stops working.

The graph below shows that the optimum temperature for an enzyme to work is 37°C. At temperatures above this the enzyme activity rapidly decrease because the enzyme is denatured.

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pH and enzymesChanges in pH also alter an enzyme’s shape. Different enzymes work best at different pH values. The optimum pH for an enzyme depends on where it normally works. For example, enzymes in the stomach have an optimum pH of about 2.

The graph below shows

Questions to test your knowledge so far:

Which can affect enzyme activity?

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What is the optimum temperature for enzymes to work at?

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What are enzymes made up from?

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Use the diagram and lock and key model to describe how enzymes work.

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