1.1 - 1.5

Magnification def

The number of times bigger the image looks compared to the real object

Real object def

The specimen you put under the microscope

Image def

What you see when you look through the microscope; the image of the real object appears magnified

Magnification formula triangle

Resolving power def

The measure of the ability to distinguish two separate points that are close together

How does a light microscope work?

It uses a beam of light to form an image

What is a light microscope’s maximum magnification?

2000x

What are the advantages of a light microscope?

• Relatively cheap

• Easy to use

• Can be used almost anywhere

• Can magnify live specimens

What is the disadvantage of light microscopes

Magnification isn’t very high: you can see cells and some structures but not the details of organelles

When was the electron microscope invented?

1930s

How does the electron microscope work?

Electron microscopes use a beam of electrons to from an image

What is the maximum magnification of an electron microscope?

2,000,000x

What are the advantages of the electron microscope?

• Scanning electron microscope (SEM) can create dramatic 3D images

• Transmission electron microscope (TEM) has very high magnification and resolution

What are some disadvantages of the electron microscope?

• Very expensive

• Hard to use

• Has to be kept in temperature, pressure and humidity controlled rooms

• Can’t magnify live specimens (specimen has to be kept in a vacuum)

How many metres is one micrometre

10^-6

How many metres is 1 nanometre

10^-9

What is the resolution of a TEM and SEM?

SEM = 10nm

TEM = 0.2nm

What is the resolution of a light microscope

200nm

What could an electron microscope be used for?

To examine sub cellular structures (eg chromosomes during cell division)

What can a light microscope be used for?

To look at cells dividing (eg stained onion cells)

Explain the importance of microscopes in the development of our understanding in cell biology (6)

• Without light microscopes we cannot see most cells

  Light microscopes

• show cellular structures of living organisms and some subcellular structures (eg nucleus and chloroplasts)

• Allows observation of living cells and staining to show features

  Electron microscopes

• Enable examination of cells in great detail

• Help determine what goes on within individual body cells

• Can only be used for dead specimens in a vacuum

When were the first light microscopes developed?

Mid 17th century

Why should you use the lowest magnification for the objective lens when you first use the microscope?

Because it is easier to focus and gives the largest field of view

How could you adjust a microscope to see an object more clearly?

Turn the fine focus knob

Ribosomes def

The area where protein synthesis takes place. All proteins needed in the cells are made here

Mitochondria def

Organelles that release the most energy during respiration

Cytoplasm def

Liquid gel where chemical reactions occur

Nucleus def

Controls the functions of a cell, contains genetic information to build new cells or organisms

Cell wall def

Made of cellulose for strength and support

Chloroplast def

Contains chlorophyll which absorbs sunlight so the plant can create food via photosynthesis

Cell membrane def

Controls the passage of substances in and out of the cell

Vacuole def

Space in the vacuole filled with sap (sugar and salt solution) which keeps cells rigid

Suggest two cells that are unlikely to have chloroplasts and why they don’t have any

• root cells - no exposure to light

• Cells in flowers of plants - their function is not to photosynthesise

What types of substances does the cell membrane control the passage of in and out of the cell?

Glucose, mineral ions, hormones and urea

Describe the differences between prokaryotic and eukaryotic cells

Prokaryotic cells

• Found in bacteria and archaea

• No nucleus

• Found in unicellular organisms

• No membrane bound organelles

• Smaller

• No membrane bound organelles

• Reproduction is asexual

• DNA is circular. Can have one or more small rings (plasmids)

• Has cell wall

Eukaryotic cells

• Found in animals and plants

• Has nucleus

• Found in multicellular organisms

• Have membrane bound organelles

• Reproduction is sexual

• DNA is linear

• Cell wall is for plants only

How big is a eukaryotic cell?

10-100 micrometres

How big is a prokaryotic cell?

1 micrometre

How big is a virus?

100 nm (nanometres)

How big is DNA?

10 nanometres (nm)

How big an atom?

1 nanometre (nm)

Put the following in size order: (smallest to largest)

• Eukaryotic cell

• Virus

• Atom

• DNA

• Prokaryotic

1. Atom

2. DNA

3. Virus

4. Prokaryotic cell

5. Eukaryotic cell

What are flagella?

Long protein strand that lashes out

State one use of a flagella in a prokaryote

Movement

Describe the similarities and differences between the features found in prokaryotic and eukaryotic plant and animal cells.

• All cells have cell membranes and cytoplasm

• Eukaryotes and prokaryotes can have a cell wall

• Prokaryotes have no nucleus and no chloroplast

• Eukaryotes have no plasmids

Evaluate the possibility that chloroplasts and mitochondria may have originally been free-living bacteria

• bacteria are 1-2 orders of magnitude smaller than eukaryotic cells

• Bacteria contain free genetic material

• Bacteria can reproduce

• Mitochondria and chloroplasts are similar in size to bacteria

• Mitochondria and chloroplasts contain free genetic material so they can reproduce independently of the cell dividing

What is the function of a sperm cell?

To transport the male DNA to the egg

Where are sperm cells found?

In the testes

What are the 3 adaptations of the sperm cells?

• A long tail to swim to the egg

• Lots of mitochondria to provide energy from respiration for the sperm to swim long distances

• An acrosome at the front of the head which stores digestive enzymes to break down the outer layer of the egg

Where are muscle cells found?

In the muscles

What is the function of muscle cells?

To contract and relax to move bones in the skeleton

What are the 3 adaptations of muscle cells?

• Special proteins slide over each other making the fibres contract

• There are many mitochondria to transfer energy

• Contain a store of glycogen which can be broken down and used in cellular respiration to transfer energy needed for fibres to contract

What is the function of nerve cells?

The function of nerve cells is to carry nerve impulses around your body

Where are nerve cells found?

In the nervous system

What are the 4 adaptations of nerve cells?

• Nerve endings (synapses) pass impulses

• Contains lots of mitochondria to make transmitter chemicals

• Long axon carries nerve impulses

• Dendrites make connections to other nerve cells

What is the function of root hair cells?

To absorb minerals and water from the soil

Where are root hair cells found?

In the roots of plants

What are the 3 adaptations of root hair cells?

• Increase surface area available for water to move into the cell

• Large permanent vacuole that speeds up the movement of water by osmosis from the soil across the root hair cell

• They have many mitochondria that transfer energy needed for the active transport of mineral ions into the root hair cells

What is the function of photosynthetic (palisade) cells?

Make food for the plant via photosynthesis

Where are palisade cells found?

In the top of the leaf

What are the 3 adaptations of palisade cells?

• Contain chloroplasts containing chlorophyll that trap the light needed for photosynthesis

• Positioned in continuous layers in the leaves and outer layers of the stem so that they absorb as much light as possible

• Large permanent vacuole that keeps the cell rigid as a result of osmosis

Why is a large permanent vacuole useful for palisade cells?

• they keep the cell rigid as a result of osmosis

• When these rigid cells are arranged together to form photosynthetic tissue, they help to support the stem

• They keep the leaf spread out to capture as much light as possible

What is the xylem?

• It is the transport tissue in plants that carries water and mineral ions from the roots to the leaves and shoots

• It also helps to support the plant

In which 2 ways are xylem cells adapted to their function?

• Xylem cells are alive when first formed but a chemical called lignin builds up spirals in the cell walls. The cells die and form long hollow tubes that allow water and mineral ions to move easily through them

• Spirals and rings of lignin make the cells very strong to withstand the pressure of water moving up the plant. They also help to support the plant stem

What is phloem?

• The specialised transport tissue that carries food made by photosynthesis around the body of the plant

• Made up of phloem cells that form tubes

What are the 2 adaptations of phloem cells?

• Cell walls between cells break down to form sieve plates. These allow water carrying dissolved food to move freely up and down the tubes

• Phloem cells lose a lot of internal structures but they are supported by companion cells that help to keep them alive. Mitochondria from companion cells transfer the energy needed to move dissolved food around the plant