7A.1 What living things are made from (HSW)assets.cambridge.org/97805217/25675/excerpt/... · Four...

17A Cells: the body’s building blocks

7A.1 What living things are made from (HSW)

OutcomesYou should already know Keywords

Question 1

Question 3

2

4

skulleye

brain

Cystis

(bladder)

Aidoion

(penis)Orchis

(testis)

cartilage

bone

bone marrow

Aristotle lived in Greece over 2000 years ago. He was very

interested in plants and animals and in how the human body works.

Look at the drawing by Aristotle of some parts of the human body.

We call these parts . Old drawings and texts from China and

the Middle East also show human organs. Some even show plant

organs.

Aristotle’s drawing.

A scan through part of the head.

Part of a thigh bone.

A closer look at human organs

In the late 18th century, a French doctor called Xavier Bichat did

hundreds of post-mortems. Post-mortems are operations carried

Bichat found that each human organ contains more than one kind

of material. He listed 21 different kinds. We call these materials

. Bichat couldn’t see the detailed structure of these tissues

because he didn’t have a microscope.

• operations

• cutting up dead bodies.

Now we can look at X-rays and body scans, too.

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2 7A Cells: the body’s building blocks

7A.2 How microscopes helped to change our ideas (HSW)

KeywordsYou should already know Outcomes

Question 1 2 3

Hooke’s drawing of cork cells.

Leeuwenhoek’s microscope.

Onion cells as seen using Robert

Brown’s microscope.

1665 Hooke published his drawings of microscopic structures.

One of the drawings was of a slice of cork. It showed

that cork is made up of what look like tiny boxes.

He called these boxes .

1683 Leeuwenhoek published his drawings of microscopic

creatures. Because his lens was so much better, the

images were clearer than Hooke’s. He could see

more details.

1831 A Scot, Robert Brown, saw and named the .

1840 German scientists, Matthias Schleiden and Theodor

Schwann, published the cell theory – that all plants and

animals are made of cells.

were invented in the 16th century but their lenses

were not very good.

Type of

microscope

Invented by About the images

simple

(1 lens)

not very clear

compound

(2 lenses)

Hans and Zacharias

Janssen (Dutch)

in 1590 and later

by Robert Hooke

(English)

better images

simple

(1 lens – but

a better one)

Antonie van

Leeuwenhoek

(Dutch) in 1673

even better – things looked

200 times larger than they

really were







Question 4 5 6 7 8

This ladybird is 4 mm long.

Scale drawings

When we draw what we see under a microscope, we draw

things much bigger than they really are. We draw them to .

We often use scale drawings in our lives, not just in science.

Maps and plans are scale diagrams. They show places smaller

than they really are. We call this scaling down.

When we show things bigger than they really are, we are

scaling up.

You can show a scale in one of these ways:

than it really is. This means you

can see more detail.

7A.2 How microscopes helped to change our ideas

20 1 mm

Under a magnifying lens, the

ladybird looks three times as

big, so the scale factor is ×3.

This is Leon’s drawing of the same ladybird.







7A.3 What cells are like


Question 1

Question 2

A

C

B

D

Four microscope views of living and non-living things.

Cells are very small

Remember that

• all living things are made of cells

• cells are so small that you need a microscope to see them.

If you magnify cells a hundred times or more, you can see smaller

parts inside them.

Non-living things show different types of structure.

Sometimes there is no detail to see under a light microscope.

Cells are not all alike

All cells are very small. But they are not all the same size.

In this square,

• 2500 rhubarb skin cells, or

• 10 000 human skin cells.

Cells also vary in shape.

Plant and animal cells look quite different under the microscope.

Plant and

animal cells.







Question 3 4

Question 5 6

cytoplasm

vacuole

nucleus

cell membrane

chloroplast

cell wall

cytoplasm

nucleus

cell membrane

A closer look at animal cells

Cells are made of lots of different parts.

Each part has a different job to do to keep the cell

• alive

• working properly.

Plant cells aren’t quite the same

Chris also made a slide of a moss leaf.

She looked at the cells under a microscope.

Chris scraped some cells

from the skin inside her

cheek.

Cells in a moss leaf.

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.







7A.4 Different cells for different jobs

Question 1

Question 2 3 4


this cell

secretes

mucus

dust carried out

of breathing tubes

tiny hairs (cilia)

mucus and dust

senses in

your fingers

very long nerve fibre connections to nerve

cells in your brain and

spinal cord

soil and

water

root hair cell

inside the

root

B

A

Two kinds of cells in breathing

tube linings.

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 they do different jobs.

The cells on the inside of the breathing tubes of humans and other

animals are similar because they do the same jobs.

Goblet cells

Called this

because...

of their shape cilia = beating hairs

epithelium = skin or lining

Job to make sticky mucus

to trap dust and

micro-organisms

to carry the mucus out of

the lungs

More specialised cells

are very long. Your brain and spinal cord send and

receive messages in the form of nerve impulses from all over

your body.

Your are full of a chemical

called haemoglobin. This can join with oxygen.

So your blood can carry oxygen to every cell in

the body.

Plants have special cells too.

are one example. The hairs give the roots a

bigger surface for absorbing water.







7A.4 Different cells for different jobs

Question 5

Question 6 7 Check your progress

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

cellsbuilding

materials

parts of

room

room

house

tissues

plant

organs

How cells work together

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.

There are many different rooms in a house.

Each room has a different purpose.

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 .

In a living thing, there are many different

organs. Each organ has a different job.

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 .

All the cells in a tissue are the same.

They work together to do the same job.







7A.5 How new cells are made

Question 1

Question 2

KeywordsOutcomesYou should already know

nucleus

specialised cell

cell

cell

Cell cycle.

People used to think that living things sometimes appeared out

of nowhere.

• They saw 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 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 cells divide.

How a cell divides

in more materials, they grow. When they are big enough, the cells

divide again. We call this the .







Question 3

Question 4

Summary

Review your work

new cell

wall forms

nucleus divides to

form two nuclei How a plant cell divides.

Unspecialised cells divide

over and over again.

Muscle cells are specialised.

They don’t divide.

Plant cell division

When a plant cell divides, it’s not just the nucleus and cytoplasm

that divide. A new cell wall forms between the new nuclei.

The nucleus of a cell holds

all the information that tells

a cell how to develop and

to work.

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 one.

The nucleus controls how a cell develops

Specialised cells

Some 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






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