Biology By Example

By Tim Prichard

Biology by Example is a revision guide aimed at the AQA GCSE science courses grades 9–1. It does have extra content, so it also covers the majority of the Edexcel and other UK exam boards as well. Biology by Example like the other guides in this series, (Physics by Example and Chemistry by Example) are different to other revision guides on the market because they are centred around practice questions with fully worked and solved solutions. This means the student/teacher can follow the method step by step of how to approach and solve exam style questions in the three sciences. Including hints, tips and common mistakes students make to help describe the approach because it is necessary to fully understand successfully answer exam style questions in GCSE science. The guides all contain self-testing sections with answers and space for working.

Biology by Example contains a huge array of different styles of questions from long answer, comprehension, multiple choice, matching sentence starters and endings, graph analysis and straightforward recall to name but a few. The three guides together have around 800 practice questions with solutions fully worked and written in an easy-to-follow way. This gives the student or teacher probably the most comphrensive source of revision material or lesson planning material for school science there is currently on the market.

• Language: English
• Publisher: Brown Dog Books
• Release date: Apr 19, 2022
• ISBN: 9781839524943

Book preview

MICROSCOPY

Microscopy as the name suggests involves using microscopes to study objects which are too small to be seen by the naked eye.

The first microscope was built by two Dutch spectacle-makers in the 1590s but later in the 1670s a Dutch lens maker called Antonie Van Leeuwenhoek designed and built a single lens microscope to study unicellular organisms such as bacteria and red blood cells. He is now recognised as the father of modern-day Microbiology.

Question 1

Label the diagram of a typical microscope which you might find in a school laboratory.

Question 2

What do we mean by Resolution or Resolving power?

Answer:

If two objects which are exceedingly small and close together, a microscope with a high resolution or resolving power can separate or distinguish between both points giving a clear image. If the microscope does not have a high resolution or resolving power, they will blur and appear to merge together.

Question 3

You will need to understand units when answering microscopy questions, so test yourself by filling in the gaps in the table below.

Answers:

Note:   or 1 billionth of a metre!

Question 4

Using the formula triangle below, make each term the subject of the equation.

Answers:

Question 5

An image of a cell in a microscope has a diameter of 2,000 µm. The actual cell has a diameter of 100 µm. What is the magnification of this microscope?

Answer:

Use the equation,

Question 6

The scale bar in the diagram measures 30 mm. This distance represents 3 µm. What is the magnification in this diagram?

Answer

•First change the mm into µm by multiplying by 1,000

•30mm × 1,000 = 30,000

•

•30,000/3 = 10,000

•Magnification = × 10,000

Question 7

A eukaryotic cell measures 5 µm in length. If the magnification is ×500, how big is the image?

Answer

Image = magnification × real size

Now convert real size into mm by dividing by 1,000

Question 8

A plant cell in a picture measures 12 mm across. If the actual size of the cell is 0.010 mm, what is the magnification?

Answer

(Both units in mm so do simple division)

Magnification is ×1,200

Question 9

A bacterial cell in a diagram measures 6 cm across. If the actual length of the bacteria cell is 4 µm, calculate the magnification of the diagram.

Answer

Note: in this question we need to change the terms into the same units, so I chose to put them both into micrometres (µm)

Question 10

a) The nucleus of an animal cell on a computer screen measures 2.5 mm across. If the magnification on the screen is ×750, what is the actual size of the nucleus?

b) Convert your answer from mm to µm

Answers

a)

b) 0.0033 × 1,000 = 3.3 µm

Question 11

A microscope is using a lens of ×6,000 magnification. If it views a bacteria cell of 5 µm across, how big will its image be in mm and in cm?

Answer

Rearrange to make image size the subject,

Image size = magnification × actual size

Image size = 6,000 × 5 µm

Image size = 30,000 µm

So, in mm the image in mm would be

Or in cm it would be

Question 12

Why do scientists sometimes use a stain such as methylene blue or iodine when looking at cells through a microscope?

Answer

The stain makes some of the organelles in a cell visible, e.g. the cell wall in an onion cell.

Question 13

Describe how you would prepare an onion cell to look at through a microscope in the classroom.

Answer

To make this answer easier to understand I have simplified it by using step-by-step bullet points.

•Peel using tweezers a thin epidermal layer from inside the onion which is nearly transparent.

•Place on a microscope slide.

•Add a drop of iodine stain so the organelles can be clearly seen.

•Lower a cover slip on top of the onion and stain slowly so as to not trap any bubbles.

•Choose an objective lens with the lowest magnification and then using the coarse focus adjust until an image is seen.

•Adjust further with the fine focus to gain a sharp clear image.

•If the image is not satisfactory, change the objective lens to the next highest magnification and repeat the focusing procedure.

PLANT AND ANIMAL CELLS

Plant and animal cells have some organelles in common like a cell membrane, but there are key differences. You will be expected to be able to draw and label each cell, describe what each organelle does and describe the differences between plant and animal cells.

Question 1

What is an organelle?

Answer

An organelle is a ‘structure’ in a cell which has a specific function or job in that cell. This is the same as organs in the body such as the heart which has a function to pump blood around the body.

Question 2

Draw and label a plant cell.

Answer

Question 3

Draw and label an animal cell.

Answer

Note: the animal cell contains a much smaller vacuole, and they are only temporary in animal cells. Depending on the course you study they may or may not be included in the animal cell diagrams, so you should check with your teacher or syllabus if the animal cell diagrams include them as some do and some don’t. It is important to remember however, plant cells always have much larger and permanent vacuole and are always included in all plant cell diagrams whichever syllabi you are following.

Question 4

Name the organelles which perform the following functions,

a) Controls the cell and contains genetic information.

b) A liquid gel where the chemical reactions take place.

c) Where aerobic respiration takes place to release energy.

d) Where proteins are made. (May be called protein synthesis.)

e) Contains chlorophyll and absorbs light.

f) It is filled with sap and supports the cell.

g) Controls the movement of substances into and out of the cell.

h) Made of cellulose and supports and strengthens the cell.

Answers

a) Nucleus

b) Cytoplasm

c) Mitochondria

d) Ribosomes

e) Chloroplasts

f) Permanent vacuole

g) Cell membrane

h) Cell wall

Question 5

What is the difference between a plant and animal cell?

Answer

Generally speaking plant cells have extra organelles which are, chloroplasts, permanent vacuole and cell wall.

Question 6

Why don’t root hair cells contain chloroplasts?

Answer

Chloroplasts contain chlorophyll to absorb light. Because a root is underground there is no light, so they are not needed.

Question 8

The chloroplasts make sugars for food in a plant, in a process which is called what?

Answer

Photosynthesis

Cell differentiation or specialisation

Multicellular organisms like mammals, flowers or even you or I contain different types of cells, all adapted to carry out a particular function (job). Because they have different functions, we say they are ‘specialised’ or ‘differentiated’ to enable them to carry out that function.

You will need to be able to describe how the structure or adaptations relate to the functions of a few plant and animal cells.

Question 1

Draw a labelled diagram of the following animal cells.

a) Sperm cell

b) Muscle cell

c) Nerve cell

Answers

Question 2

For the following descriptions of animal cells say if it is a sperm, muscle or nerve cell.

a) They have long thin bodies called axons with finger like extensions at the end called dendrites. They carry electrical impulses around your body.

b) They can swim in the female reproductive system as they have long tails and use a lot of energy. Because they use a lot of energy, they contain a lot of mitochondria.

c) They are able to contract and relax. They work together forming tissue. They work in pairs to enable movement of limbs such as arms and legs.

Answers

a) Nerve cell

b) Sperm cell

c) Muscle cell

Question 3

Draw a labelled diagram of the following cells,

a) Root hair cell

b) Xylem cell

c) Phloem cell

Answers