Cell Structures (OCR Gateway GCSE Biology: Combined Science)

The diagram shows cells that are important in the process of transpiration in plants.

The diameter of cell X has been magnified 500× and it measures 20 mm across.

Calculate the actual diameter of cell X.

Use the equation: actual diameter = measured size ÷ magnification

Diameter = ................................................... mm 

What is the name of plant cell X?

Tick (✓) one box.

State two ways that cell X is adapted to its function in a plant.

1 ..........................................................

2 ...........................................................

Light microscopes let us see objects as small as 0.2 micrometres.

The diameter of cells similar to cell X, can vary between 0.008mm and 0.5mm.

(1mm = 1000 micrometres)

Is it possible to see all these types of cells using a light microscope?

Explain your answer.

State why electron microscopy has increased our knowledge of sub-cellular structures.

Look at the diagram showing a plant cell.

(i)

The diameter of the nucleus in the diagram is 10 millimetres. The actual size of the nucleus is 10 micrometres.

Calculate the magnification of the diagram.

Answer = ....................................... × [2]

(ii)

Look at the picture of part of a plant cell.

Use the arrow (measuring 75 mm) on the picture and the scale (measuring 15 mm) to estimate the length of the chloroplast.

Answer = ....................................... μm [1]

A scientist clones a cauliflower plant.

He uses small pieces of the cauliflower plant called explants.

• This is the method the scientist uses to get the explants:
•  Place the equipment in a beaker of bleach and swab the bench with 70% alcohol.
• Collect a small piece of cauliflower and place on a white tile.
• Using a scalpel cut the piece of cauliflower lengthways into small 3–5mm pieces called explants.
• Measure the mass of the explants.

What equipment should be used to measure the mass of the explants to 1 hundredth of a gram?

The scientist prepares the explants for cloning on an agar jelly plate.

He does this by placing the explants on the agar.

To grow the explants into cauliflower plants, the scientist places the agar jelly plate in a warm room near to a window.

(i)

Before they form new plant structures, the explants must take in sugars from the agar jelly.

Explain why explants cannot make their own sugars.

 [2]

(ii)

The experiment could be improved by placing the agar jelly plate with explants into a heated cabinet containing light bulbs.

Describe how this cabinet could be further improved to maximise the growth and development of the explants.

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The scientist observes some of the tissues of the growing explants using a light microscope.

The diagram shows some of the plant cells.

The diameter of X has been magnified 500× and measures 20 mm across.

What is the actual diameter of X?

Give your answer in standard form.

Diameter = ................................. mm

Transmission electron microscopes (TEM) work by passing a beam of electrons through a very thin slice of an object.

Suggest one advantage and one disadvantage of using TEM rather than a light microscope to look at cells.

advantage ...............................
disadvantage .........................