7a.3 what cells are like a closer look at animal cells

57A Cells: the body’s building blocks

Question 3 4

Question 5 6 7 8

Question 9Question 9

cytoplasm

vacuole

nucleuscell membrane

chloroplast

cell wall

cytoplasm

nucleus

cell membrane

Rhubarb plant.

rhubarbleaf stalk

A closer look at animal cellsCells are made of lots of different parts. Each part has a different job to do to keep the cell alive and working properly.

Chris made a slide of some cheek cells.

The picture shows what they looked like under the microscope.

Plant cells aren’t quite the sameChris also made a slide of a moss leaf.

The picture shows what the cells looked like under a microscope.

Plant cells vary too.

Chris scraped some cells from the skin inside her cheek.

Cells in a moss leaf.

Microscope view of rhubarb leaf stalk cells.

7A.3 What cells are like

Under the microscope the cells look coloured. The colour is a stain that makes them show up more clearly.

A moss plant.

Cheek cells.

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6 7A Cells: the body’s building blocks

7A.4 Different cells for different jobs

Question 1

Question 2 3 4

KeywordsYou should already know Outcomes

this cellsecretesmucus

dust carried outof breathing tubes

tiny hairs (cilia)

mucus and dust

senses inyour fingers

very long nerve fibreconnections to nerve cells in

your brain and spinal cord

soil and water

root hair cell

inside theroot

B

A

What the lining of your windpipe looks like.

There are over a million different types of animal. They all have different shapes and sizes. But in all these animals, there are only about 200 different kinds of cell. These cells are different because of the jobs they do, not because of the kind of animal they are found in.

Each kind of cell can do the same job in lots of different animals.

For example, when you breathe in air, you breathe in dust and micro-organisms too. They can harm your lungs. Two kinds of cells on the inside of the breathing tubes of humans and other animals help to stop this happening.

One kind makes the lining sticky with mucus. Dust and micro-organisms get trapped in this mucus. We call these cells goblet cells because of their shape. The other kind has tiny hairs that carry the mucus out of your lungs. We call these cells ciliated epithelial cells. (Cilia = beating hairs. Epithelium = skin or lining.)

More specialised cells

Nerve cells are very long. They carry messages in the form of nerve impulses from one part of your body to another. Your brain and spinal cord send and receive nerve impulses from all over your body.

Red blood cells are full of a chemical called haemoglobin. This can combine with oxygen.So red blood cells can carry oxygen to everycell in the body.

It’s not just animals that have special cells. Plants take water in through special cells in their roots. They are called root hair cells. The hairs give them a bigger surface for absorbing water.







7A.4 Different cells for different jobs

Question 5

Question 6 7 8

Check your progress

buildingmaterials

parts ofroom

room

house

cells

tissues

plant

organs

How cells work together

In a house, different groups of building materials are joined together to make the rooms. In a living thing, several tissues are joined together to make an organ.

There are many different rooms in a house, and each room is needed for a different reason. In a living thing there are many different organs, and each organ has a different job.

A house doesn’t look like a living thing. However, the way the building materials of a house are grouped is similar to the way that cells in a living thing are organised.

The bricks in a house are like the cells in a living thing. A group of bricks is called a wall. A group of similar cells is called a tissue. All the cells in a tissue are the same and work together to do the same job.

How building materials build up into a house. How cells build up into a plant.







7A.5 How new cells are made

Question 1

Question 2

KeywordsOutcomesYou should already know

nucleus

specialised cell

cell

cell

The cell cycle.

People used to think that living things sometimes appeared out of nowhere. They saw for themselves that maggots appear in rotting meat. Leeuwenhoek described tiny living animals in rotting things. So the idea seemed to be sensible.

In the 19th century, Louis Pasteur proved that this idea was wrong.He showed that living things come only from other living things.

Cells are the building blocks of life. Like all living things, they don’t just appear from nowhere either.

In 1858, a German scientist called Rudolph Virchow suggested that new cells could only grow from cells that were already there. Now we know that new cells form only when existing cells divide.

How a cell divides

materials, they grow. When they are big enough, the cells divide again. We call this the cell cycle.







Question 3

Question 5

4

Summary

Review your work

Muscle cells are specialised.They don’t divide.

new cellwall forms

nucleus divides toform two nuclei How a plant cell divides.

Unspecialised cells divide over and over again.

Plant cell divisionWhen a plant cell divides, it’s not just the nucleus and cytoplasm that

The nucleus controls how a cell developsThe nucleus of a cell holds all the information that tells a cell how to work and develop. Before it divides, the nucleus makes a copy of this information. One copy goes into each new nucleus. So the new cells are identical to the old ones.

Specialised cellsSome cells divide over and over again, but other cells become specialised to do particular jobs. Specialised cells don’t divide again.

7A.5 How new cells are made







7A.HSW How ideas change

KeywordsYou should already know Outcomes

Question 4

Question 1

Question 2 3

Studying cells is part of biology

Studying light and optics is part of physics.

Applying science is technology.

The story of cells shows the importance of working together.

New evidence, new explanations

You have seen how ideas about the tissues of the human body changed following technological developments.

recognising tissues

discovery of cells

parts discovered inside cells.

Invention of the microscope.

Observation under a microscope

Improvement of microscopes

Observation with the naked eye

One theory that came out of Abbe’s experiments was a limit to what can be seen clearly using a light microscope. He predicted that future ‘microscopes’ might not limited by the properties of light. That prediction came true with the invention of electron microscopes. These use a beam of electrons rather than light.

During the 17th and early 18th centuries, people improved both lenses and microscopes. Only after German instrument manufacturer Carl Zeiss teamed up with Ernst Abbe in 1866 did the next big change take place. Zeiss asked Abbe to use optics theory to design a better microscope.

experiments, not just with lenses but on what happens to light as it passes through lenses to form an image. From a series of experiments, he was able:

• to suggest a theory about how microscope images formed;• to test his theory by doing more experiments;• then to put his theory into practice in his designs.

Scientists gather evidence by observing and experimenting.

They use the evidence to make theories – and then gather more evidence to test those theories.

Just like detectives, scientists try to explain the evidence that they collect.

They suggest theories based on the evidence they have at the time.

With new evidence, they may change their ideas and suggest new theories.






11

7A.HSW How ideas change


Question 5 6

A homunculus in a sperm.(The plural is homunculi.)

Changing ideas about babiesIdeas about where babies come from also changed with the invention of the microscope.

If you had lived more than 250 years ago, you probably didn’t know exactly where babies came from. Look at the table.

Evidence Who and when Fluid passed from a man into a woman tomake a baby contains …

was involved.Hippocrates … tiny body parts.

Under a microscope, they could see tiny swimming things in semen.

Antonie van Leeuwenhoek, Nicolas Hartsoeker, others

… ‘animalcules’. Some scientists claimed to see miniature humans inside the animalcules from humans. They were called homunculi, the Latin world for ‘little men’.

Experiments showed that both sperm and egg cell were needed to make a baby.

Lazzaro Spallanzani … sperm that joined with a woman’s egg cell.

New evidence changed ideas about reproduction.






7a.3 what cells are like a closer look at animal cells

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