© Boardworks Ltd 20071 of 39. © Boardworks Ltd 20072 of 39

© Boardworks Ltd 20071 of 39



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 0.025 µm and 60

µm 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 1,000 µm 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.

oxygencarbondioxide

glucose + + 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.

carbondioxide + 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


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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