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Cells - PowerPoint PPT Presentation

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Cells. Where in the world?. How does a cell resemble a city?. What is a cell?. A cell is the basic unit of life, from which larger structures such as tissue and organs are made. Unicellular organisms, such as bacteria, consist of just a single cell.

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Where in the world
Where in the world?

How does a cell resemble a city?

What is a cell
What is a cell?

A cell is the basic unit of life, from which larger structures such as tissue and organs are made.

  • Unicellular organisms, such as bacteria, consist of just a single cell.

  • Multicellular organisms consist of many cells – humans are made from an estimated 50 trillion cells!

How big is a cell
How big is a cell?

Most plant and animal cells are between 10µm and

100µm in size – around 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 100µm

in diameter.

The smallest human cell is the sperm cell – the head is around 5 µm long.


Thanks to advances in microscope technology, we can see micro-organisms with far greater detail and clarity than was possible in the past.

size of image

actual size of the object

magnification =

When Antonie van Leeuwenhoek discovered single-celled organisms in 1676, his microscope could magnify an image up to 500 times. Now, with the use of electron microscopes, scientists can attain a magnification as high as 2×106.

Specialized cells
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.


Unlike other cells, bacteria have no distinct nucleus. Instead, their genetic material is contained within a coiled cluster of chromosomal DNA and a single circular strand of plasmid DNA.

Plasmid DNA can reproduce independently of chromosomal DNA, and can be transferred to other cells.

Bacteria also lack mitochondria and chloroplasts. Some bacteria have one or more flagella, which are used for locomotion.

What is a cell wall
What is a cell wall?

All plant cells have a cell wall –a rigid layer that surrounds the cell membrane.

The plant cell wall is made from cellulose, a carbohydrate polymer. The purpose of the cell wall is to:

  • maintain the shape and structure of the cell

  • protect the cell’s contents from pathogens

  • prevent damage to the cell caused by excess water intake.

Unlike the cell membrane, the cell wall is freely permeable to water and other molecules.

What is a vacuole
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:

  • storing waste products

  • maintaining the water and pH balance of the cell

  • maintaining the shape of the cell.

The size of vacuoles depend on how much water the plant has absorbed.

What are chloroplasts
What are chloroplasts?

Chloroplasts are the site of photosynthesis in plant cells.

A green pigment in chloroplasts called chlorophyll absorbs the energy in sunlight.

This energy is used to convert carbon dioxide and water into glucose and oxygen.

Make a cell model
Make a cell model

You can make your own 3-D cell using the following items:

  • a plastic bag

  • clear gelatin

  • small objects to suspend in the cellulose paste (these will represent the internal structures of the cell).

Can you make a model of a typical plant or animal cell?