BTEC First Principles of Applied Science12

1.1 Cells – structure and function

Organelles – Small structures within cells. Each carries out a particular function.

Key term �How are we made?All living things on Earth are made of cells. Some consist of just one cell but some, like you, are made of many cells. Cells are the building blocks of organisms. Cells are very small but you can see them with a microscope.

The structure of a typical plant cell. The structure of a typical animal cell.

Lesson 4.4 discusses how viruses are not made of cells.

Link

Sue is a cytology screener. She works in a hospital laboratory and has to look at microscope slides of cells to see if any are abnormal. This could indicate that the person whose cells they are has early stage cancer. Sue has to know about cell structure so she can tell abnormal cells from normal ones. Cytology is the study of cell structure.

Case study

outer cellmembrane

cell wall

cytoplasm

large �uid-lledvacuole

mitochondrionnucleus

chloroplastouter cellmembrane

cytoplasm

mitochondria

nucleus

Plant and animal cells are called eukaryotic cells. Eukaryotic organisms have cells with their genetic material enclosed in a nucleus. Nearly all of the living things on Earth, except bacteria, are eukaryotes.

Did you know?

A microscope slide showing abnormal (red) and normal cells from the cervix.

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UNIT 1 Principles of Science

Cell component

Function In plant cells?

In animal cells?

Outer cell membrane

Encloses the cell and keeps it separate from its environment. It controls how substances enter and leave the cell.

3 3

Nucleus Contains DNA (genetic information) arranged into chromosomes. It controls the activities of the cell.

3 3

Cytoplasm Jelly-like substance in which the organelles are held. Many chemical reactions take place in the cytoplasm.

3 3

Mitochondrion (plural: mitochondria)

The organelle where aerobic respiration – the release of energy from glucose or fat in the presence of oxygen – takes place.

3 3

Cell wall Made from cellulose. The cell wall is very strong and prevents the cell from bursting. It gives the cell shape.

3 7

Chloroplast Contains chlorophyll, which absorbs light energy for photosynthesis.

3 7

Vacuole Contains cell sap and provides extra support for the cell. The vacuole can store nutrients and waste products.

3 7

Many people think that plants do not have genes. Their cells contain a nucleus, with DNA organised into chromosomes. Genes are lengths of DNA. So plants do have genes.

Common misconception

Lesson outcomes

You should know about the basic structure and function of some eukaryotic cells and of some of their components.

Activity A

List the ways that animal and plant cells are (a) similar to each other and (b) different from each other.

For each of the following statements, say whether it is true or false.1 All living things are made of many eukaryotic cells.2 Plant cells do not contain mitochondria.3 Animal cells do not have a large vacuole.4 The cell membrane controls which substances enter and leave a cell.

Just checking

Plant and animal cells have many components, called organelles, such as chloroplasts and mitochondria. The table shows the different functions of the organelles found in plant and animal cells.

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BTEC First Principles of Applied Science14

1.2 Specialised cellsYou, like many other organisms including plants, started life as a single cell – a fertilised egg. This divides and forms an embryo. Cells become specialised to perform different functions. This is called differentiation (becoming different).

Some examples of specialised cells are shown below. (a) to (f) are animal cells and (g) to (j) are plant cells. They all have the same basic components but each type has some differences in structure. These differences enable the cells to carry out their particular function (job). Each type of cell is adapted for its function.

outer cell membrane

Egg cell – for sexual reproduction.

large amountof cytoplasm

nucleus

(a)

mitochondria

(b) Sperm cell – for sexual reproduction.

very small amountof cytoplasm

tail head

nucleus

mitochondria

The sperm has a tail to help it move to �nd the egg. It also has a large number of mitochondria to supply the energy needed for the movement.

(c) Red blood cells – small cells, packed with haemoglobinwhich carriesoxygen. They have no nucleus, no mitochondriaand little cytoplasm in order to carry more oxygen.

outer cellmembrane

(d) White blood cells – for defence against infection.

nucleus

There are dierent types of white blood cell, butthey all have a nucleus, cell membrane, cytoplasmand mitochondria.

(e) Sensory neurone – long �bres carry impulses from sensory receptors to brain and spinal cord.

cell body

fatty sheath long �bre

direction of impulse

nucleus

cell membrane

receptor in skin

(f) Motor neurone – long �bres carry impulses from brain or spinal cord to muscles or glands.

cell body fatty sheath

long �bre

muscle �bresdirection of impulsedendrites

nucleus

(g) Root hair cell – for absorption.

vacuole

Extension of cell increasessurface area for absorption ofwater and minerals from soil.

outer cellmembrane

cell wall

(h) Xylem – to carry water. There is no cytoplasm or organelles.

cell wall with ligninto make it strong

empty hollow vessel forcarrying water from rootsto rest of plant

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UNIT 1 Principles of Science

i) Phloem – carries dissolved sugars from leaves to other parts of plant.

nucleus

companion cellwith organelles

sievetube

sieveplate

(j) Guard cells in epidermis of leaf – to allow carbon dioxide to enter for photosynthesis.

cell wall

cytoplasm

chloroplasts

pore openepidermal cells

nucleus

guard cells

Type of tissue

Where found in the body Functions

Epithelial (covering tissues)

Outside of skin. Make up the inside linings of heart, blood vessels, airways and gut. Some epithelial cells have tiny hairs, called cilia, on them.

Protection, absorption, filtration and excretion.

Glands are also made of epithelial cells.

Production of useful substances, such as saliva, hormones and mucus.

Connective Bone Makes up skeleton – supports you and allows you to move.

Blood Transport and defence against invading microorganisms.

Muscle Smooth muscle in walls of blood vessels and gut

Able to contract – arteries pulsate. Gut moves food through it.

Heart muscle Heart beats to pump blood around body.

Nervous Nerves, spinal cord and brain For sensing and responding in a coordinated way to the environment.

�TissuesA tissue is a group of similar, specialised cells that work together to carry out a particular function in the body. Some examples of animal tissues are given in the table below.

For each of the following statements, say whether it is true or false.1 Red blood cells cannot carry out aerobic respiration because they do not have

mitochondria.2 Neurones are the longest cells in your body.3 Blood and bone are types of connective tissue.

Just checking

Lesson outcomes

You should know how cells become adapted to carry out specific functions, and that cells form tissues.

Activity A

1 Draw large, clear diagrams of one specialised animal cell and one specialised plant cell.

2 Label and annotate (write notes next to the labels) the diagrams to show how each cell is adapted for its function. You should also research, using the Internet and textbooks, to find out more about how the cells you have chosen are adapted. Use a ruler to draw the label lines.

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