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Where in the world?

How does a cell resemble a city?


What is a cell?

Multicellular organisms

consists of many cells –

humans are made from an

estimated 50 trillion cells!

Unicellular organisms,

such as bacteria, consist of

just a single cell.

A cell is the basic unit of life, from which larger structures

such as tissue and organs are made.


How big is a cell?

Most plant and animal cells are between 0.025µm and

60µm in size – around half the diameter of a human hair

– and too small to see without a microscope.

The largest cell in the human

body is the female egg cell,

(ovum) at around 1,000µm

in diameter.

The smallest human cell is

the sperm cell – the head is

around 5 µm long.


Specialized cells

Most plants and animals are multicellular. The human

body is made up of around 200 different types of cell, all

working together.

Most cells are specialized, meaning

that each type of cell has a specific

structure and function.

All cells with a nucleus contain the

same genes, but different cells

activate different genes so they only

produce the proteins they need.

However, all cells have certain

common features and structures

called organelles.


What do cells contain?


Animal or plant?


A closer look at animal cells


Exploring animal cells


How do animal cells specialize?

red blood cell

In animals, the first type of cells in the developing embryo

are stem cells. These are unspecialized cells that go on to

form all the different cell types in the adult.

muscle cell

stem cell sperm cell

nerve cell


How are animal cells adapted?


Animal cells: fit for a purpose


A closer look at plant cells


Exploring plant cells


How do plant cells specialize?

Unlike animals, many plant cells retain the ability to

differentiate and specialize throughout their life. These

cells are found in tissues called meristems.

sieve cell

leaf cellroot cell

meristem cell


How are plant cells adapted?


Plant cells: fit for a purpose


What is a cell wall?

All plant cells have a cell wall –

a rigid layer that surrounds the

cell membrane.

Unlike the cell membrane, the cell wall is freely

permeable to water and other molecules.

maintain the shape and structure of the cell

The plant cell wall is made

from cellulose, a carbohydrate

polymer. The purpose of the

cell wall is to:

protect the cell’s contents from pathogens

prevent damage to the cell caused by excess water intake.


What is a vacuole?

The vacuole is a fluid–filled

sac found within plant cells

and some bacteria.

The vacuole has a range of

functions, including:

The site of vacuoles depend on how much water the plant

has absorbed.

storing waste products

regulating the turgor pressure of the cell.

maintaining the water and pH balance of the cell


What are chloroplasts?

Chloroplasts are the site of photosynthesis

in plant cells.

thylakoids

A green pigment in chloroplasts

called chlorophyll absorbs the

energy in sunlight.

Chlorophyll is embedded in disk-like structures called

thylakoids, which are arranged into stacks.

This energy is used to

convert carbon dioxide

and water into glucose

and oxygen.


Which organelle?


How do cells get their energy?

All organisms need energy

to survive.

Animals obtain their energy

from the food they eat, but

plants can make their own

food by photosynthesis.

In both cases, however,

energy must first be converted

into a form that can easily be

used by cells. This process is

called respiration.


Where does respiration take place?

Mitochondria are cellular organelles in which

respiration takes place.

Mitochondria use enzymes to

convert the energy from glucose

into ATP – the basic energy

source for all cells.

Mitochondria have an inner

membrane on which the

enzymes are embedded.

This membrane is highly folded to increase the surface

area on which respiration can take place.


What is aerobic respiration?

Aerobic respiration is the process of releasing energy

through the oxidation of glucose molecules.

Aerobic respiration is summarized by the equation:

This reaction releases energy in the form of ATP – a

compound that can readily be used in cellular processes.

oxygencarbon

dioxideglucose + + water ( energy)+

6O2 6CO2C6H12O6 + + 6H20 ( ATP)+


What is anaerobic respiration?

Anaerobic respiration takes place without oxygen, and

releases less energy than aerobic respiration because

glucose molecules are only partially broken down.

During strenuous exercise, cells

are deprived of oxygen but still

need energy to work. The body

responds by converting glucose

into lactic acid and energy,

leading to an oxygen ‘debt’.

Lactic acid causes muscle cramps.

When exercise stops, oxygen

levels rise, paying off the oxygen

debt and oxidising the lactic acid.


How is energy used?

The chemical energy produced by respiration, ATP, is used

by cells to undertake work.

movement – enabling muscles

to contract

Where might ATP be used?

thermoregulation in mammals

and birds

active transport – moving molecules against a

concentration gradient.

biosynthesis – building new

molecules, cells and tissues


What is photosynthesis?

Photosynthesis is a chemical reaction where light energy is

used to convert carbon dioxide and water into glucose and

oxygen.

This reaction can be summarized by the equation:

The reaction uses light energy from the Sun and takes place

in chloroplasts of plant cells.

carbon

dioxide+ water oxygenglucose +

6CO2 + 6H20 6O2C6H12O6 +

light energy

chlorophyll


Using energy from photosynthesis

The glucose produced by photosynthesis has many uses

in plants, such as for:

energy release in respiration

making cellulose for cell walls

combining with minerals to make

proteins and other essential

compounds

an energy store in the form of

insoluble starch.


Protein synthesis


Glossary (1/2)

aerobic respiration – The process of releasing energy

through the oxidation of glucose molecules.

anaerobic respiration – The process of releasing

energy from glucose molecules in the absence of oxygen.

ATP – Adenosine triphosphate, the major form of energy

used by cells.

cell – The basic structural and functional unit of life.

cell membrane – The partially-permeable barrier that

regulates substances entering and leaving a cell.

cell wall – The rigid external coat that protects and

supports plant cells.

chlorophyll – The green pigment found in chloroplasts.


Glossary (2/2)

chloroplast – The site of photosynthesis in plant cells.

cytoplasm – The jelly-like material in which all a cell’s

organelles are found, and in which most cellular processes

and reactions occur.

mitochondria – The site of energy release by respiration.

nucleus – The location of a cell’s DNA.

photosynthesis – The chemical reaction in which light

energy is used to convert carbon dioxide and water into

glucose and oxygen.

ribosome – The site of protein synthesis.

vacuole – The fluid-filled cavity found in plant cells that

stores water and nutrients.


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