yr 8 science - cells + microscopes

What is a cell?

• Cells are the basic units of all living things

• The first cell appeared on Earth about 3.5 billion years ago.

• Today, through evolution, there are many different types of cells

• Although cells vary in their size, shape and contents, they are all important in keeping an organism alive

History of cells

• Cells were discovered about 400 years ago with the invention of the microscope

• As they are so small, it is impossible to see cells with the naked eye.

• Robert Hooke discovered cells in 1665 using a cork’s microscopical cavities

Cell theory

• Three main points of cell theory:

  1. All organisms are composed of cells

  2. All cells come from pre-existing cells (biogenesis)

  3. The cell is the smallest living organism

Cell organelles

What is an organelle?

• Cell sare the building blocks that made up all living things.

• Organisms may be made up of one cell (unicellular) or many cells (multicellular)

• All cells contain small structures called organelles that have particular jobs within the cell.

• Organelles are like organs in the human body. They are small parts of a larger system

• The presence and absence of particular organelles allow us to classify cells.

Nucleus

• Control centre of the cell

• Contains genetic information (DNA) which are instructions for the cell

• Found in both animal and plant cells

Cell membrane

• Controls movements of substances into and out of a cell

• Holds the cell contents

• Found in both animal and plant cells

Cell wall

• Supports, strengthens and protects cells

• Not found in animal cells, only in plants, bacteria and fungi

Mitochondria

• Supply the cell with energy (act like a powerhouse ) using oxygen and food

• Involved in cellular respiration.

• Mitochondrion = plural

• More active cells have larger numbers (e.g. muscles)

• Found in both animal and plant cells

Chloroplast

• Absorb light from the sun to use in photosynthesis (how plants make food i.e. sugars : glucose)

• Contains a green pigment called chlorophyll which give plants their colour

• Only found in plant cells

Prokaryotes & Eukaryotes

Prokaryotes

• Prokaryote cells were the first type of cell to appear on Earth.

• They are characterised by having no nucleus, or other membrane bound organelles

• Bacteria are a type of prokaryote.

Eukaryotes

• Eukaryotic cells appeared on Earth billions of years after prokaryotes.

• Eukaryotic organisms are made up of cells containing a nucleus and other membrane bound organelles.

Microscopes

• Microscopes are a scientific tool, used to make things appear bigger

• This enables us to see objects (such as cells) thaat would otherwise be invisible to the naked eye

Light or Electron

• There are two main types of microscopes

  1. Light microscopes: These use light bouncing off the specimen to enable us to see it

  2. Electron microscopes: These use tiny particles called electrons

• The type of microscope we us depends on the size of the sample and the magnification we require.

• A light microscope may also be monocular (using one eye) or binocular (using two eyes)

Magnification

• A sophisticated light microscope can magnify objects up to around 1500 times

• Microscopes have two lenses, the objective (close as to sample object) and the ocular or eyepiece lens (where you eye goes)

• Each lens has a number on it that tells you its magnification

• Multiplying the eyepiece number by the objective lens number will give you the magnification of the microscope.

Comparing magnification

• We can see better with higher powers of magnification, but we cannot see as much of the image

Cell Specialisation

Unicellular organisms

• Organisms made up only one cell

• Also called single celled organisms

• E.g. Bacteria, paramecium, amoeba and algae.

Multicellular organisms

• Multicellular organisms are made up of many cells

• These cells are specialised to do specific functions. E.g. Fat cells, muscle cells, heart cells and nerve cells.

Muscle cells

• There are three types of muscle cells: skeletal, smooth and cardiac

  • Skeletal muscles are attached to bone and enable voluntary movement

  • Smooth muscles are attached to vital organs and function involuntarily e.g. the digestive system

  • Cardiac muscles: regulate the heart (these muscles never become tired).

Nerve cells

• Nerve cells are the units of the nervous system (the electrical wiring of the body)

• They carry messages to the brain (for processing) and to cells to carry out a response

• They carry messages away from the brain to enable movement or a response to environmental changes

Blood cells

• Red blood cells – carry oxygen around the body. They are shaped like concave disks so that the oxygen can diffuse in quickly.

• White blood cells – fight infection

Fat cells

• Fat cells have three key functions (depending on the type of fat cells)

  1. The store energy and supply the body with energy

  2. They insulate the body (and keep it warm)

  3. The provide some necessary ´padding´ or protection for vital organs

• Brown fat cells produce heat for the body

• White fat cells insulate the body and provide energy for the body.

Stem cells

• Can turn into many different types of cells

Tissue

• A large mass of similar cells that make up part of an organism and that perform a particular function.

  • Epithelial tissue: cells that form surfaces over other organs e.g. skin

  • Connective tissue: supports and holds other tissue together e.g. fat, tendons, ligaments.

  • Muscle tissue: can contract or expand becoming shorter and fatter or longer and thinner

  • Nervous tissue: send electrical signals around the body.

Organ

• A collection of two or more types of tissue working together with a similar function.

System

• A group of organs working together to perform a specific function or task.

• Examples : respiratory, skeletal, nervous, reproductive, excretory systems