Units and scale in cells

Figure 7 shows a type of bacteria (Lactobacillus acidophilus) that is found in cow’s milk.

The magnification of this image is ×18 000.

Measure the length of the bacterium labelled A.

Use your measurement to calculate the actual length of this bacterium in millimetres.

Give your answer in standard form.

Figure 8 shows the growth rate of two species of bacteria at different pH values.

State a pH that allows the growth of both Lactobacillus acidophilus and S taphylococcus aureus.

Describe the relationship between pH and the growth of Staphylococcus aureus, as shown in Figure 8.

A student investigated the effect of temperature on the decay of milk.

Milk was placed in a beaker in a water bath at 5 °C for 72 hours.

The pH of the milk was measured every 24 hours using a pH probe.

The investigation was repeated at different temperatures.

Figure 9 shows the results of this investigation.

Which is a variable that the student needs to control in this investigation?

Describe the changes in the pH of the milk at 30 °C from 0 hours to 72 hours, as shown in Figure 9.

Calculate the rate of decay of the milk at 20 °C for the 72 hours of this investigation.

Use the equation:

_........ change in pH per hour

Figure 7 shows images of two stone tools.

Scientists think that tool A was probably used by Homo erectus around 1.6 million years ago.

Tool B was probably used by Homo habilis around 2 million years ago.

Give one reason, using Figure 7, why scientists think that tool A was used by a more recent human ancestor.

Describe how scientists can date stone tools using information from where the tools were discovered.

Differences in fossilised bones indicate structural changes that have occurred during the evolution of humans.

Describe two structural changes that have occurred during human evolution.

The migration patterns of humans can be tracked by analysing DNA in mitochondria.

Figure 8 shows a mitochondrion viewed using an electron microscope.

At a magnification of 62 000 this mitochondrion has a length of 434 mm.

Calculate the actual length of this mitochondrion.

Give your answer in micrometres (µ m).

Explain why an electron microscope is used to see mitochondria clearly.

Figure 1 shows an animal cell.

Which part of the cell is labelled Y?

Which structures are found in the part labelled Z?

Name the part of an animal cell where respiration occurs.

A microscope can be used to observe the structure of a cell.

Figure 2 shows a microscope.

Give one advantage of using a microscope to look at cells.

Draw one straight line from each part of the microscope to its function.

Figure 3 shows some of the units used when cells and organelles are measured.

Give the name of the smallest unit shown in Figure 3.

A student investigated the movement of water in potatoes.

The student used three identical cubes of potato.

The size of a cube is shown in Figure 12.

Calculate the volume of this cube.

Include the units in your answer.

One cube was placed in water and each of the other two cubes were placed in solutions with different concentrations of salt.

The cubes were left for 20 minutes.

Figure 13 shows the student’s results.

Give one way the student could ensure the measurement of the mass of the cubes is accurate.

Explain the mass change in the cube in the concentrated salt solution.

The student wanted to find the concentration of salt solution where the potato cube did not change mass.

Describe how the student could modify this investigation to find this concentration.

Explain why potato cells do not burst when placed in water.

Figure 16 shows a photomicrograph of two stomata in a leaf.

The length of one guard cell in this image is 6 mm.

Convert the length of this guard cell into micrometres (µ m).

The image has been magnified 150×.

Calculate the actual size of the guard cell.

Give your answer in standard form in mm.

Explain the role of denitrifying bacteria in the nitrogen cycle.

*(c) Describe how carbon is cycled through the biotic and abiotic components of an ecosystem.

Figure 18 shows two light receptor cells from the human eye.

Which part of the eye contains light receptor cells?

These cells require energy.

The cell organelles labelled X release energy during respiration.

Name the organelles labelled X.

The cell organelle labelled Y contains chromosomes.

Name the organelle labelled Y.

Cell A responds to dim light and is responsible for night vision.

Name cell A.

Describe how the role of light receptor cell B is different from the role of light receptor cell A.

The optic nerve carries information from the back of the eye to the brain.

The optic nerve is 47 mm in length.

Nerve impulses travel at 75 metres per second.

Calculate the time an impulse takes to travel the length of the optic nerve. Use the equation: speed =

The impulse travels to the occipital lobe of the brain. The occipital lobe is labelled in Figure 19.

Which part of the brain contains the occipital lobe?

State the sense most likely to be affected if the occipital lobe is damaged.

Figure 3 shows two light receptor cells from the human eye.

Which part of the eye contains light receptor cells?

These cells require energy.

The cell organelles labelled X release energy during respiration.

Name the organelles labelled X.

The cell organelle labelled Y contains chromosomes.

Name the organelle labelled Y.

Cell A responds to dim light and is responsible for night vision.

Name cell A.

Describe how the role of light receptor cell B is different from the role of light receptor cell A.

The optic nerve carries information from the back of the eye to the brain.

The optic nerve is 47 mm in length.

Nerve impulses travel at 75 metres per second.

Calculate the time an impulse takes to travel the length of the optic nerve. Use the equation: speed =

The impulse travels to the occipital lobe of the brain. The occipital lobe is labelled in Figure 4.

Which part of the brain contains the occipital lobe?

State the sense most likely to be affected if the occipital lobe is damaged.

2 (a) Blood contains red blood cells, white blood cells, plasma and platelets.

(i) Draw one straight line from each part of the blood to its function.

part of the blood function

Figure 2 shows some red blood cells.

(Source: © SciePro/Shutterstock)

Figure 2

(ii) State two features that can be seen in the red blood cells in Figure 2.

(b) Lymphocytes are white blood cells that produce large amounts of protein.

(i) Which organelle is needed to produce large amounts of protein?

A small lymphocyte has a diameter of 10 µ m (micrometres). A microscope magnifies this lymphocyte 400 times.

(ii) Calculate the diameter of the image of the lymphocyte seen using this microscope.

image size_{..............................................................}

(iii) How many micrometres are in 1 mm (millimetre)?

5 (a) Figure 8 shows a cross-section of a root nodule on a leguminous plant. Bacteria in the root nodule provide the leguminous plant with nitrogen compounds. The leguminous plant provides the bacteria with sugars.

(Source: © Nigel Downer / Science Photo Library)

Figure 8

(i) Which term describes the relationship between this leguminous plant and the bacteria?

(ii) The width of this root nodule is 7.5 mm. Give the width in µ m.

(b) Figure 9 shows part of the nitrogen cycle.

(i) Identify the types of microorganism involved in process X and process Y.

(ii) Explain how crop rotation increases nitrate levels in the soil.

(iii) Explain why increased nitrate levels in the soil improve crop yield.

5 (a) Figure 7 shows cells from an onion root tip as seen using a light microscope.

(Source: © Rattiya Thongdumhyu/Shutterstock)

Figure 7

(i) Identify the stages of mitosis shown in cell Q and cell R.

(ii) Describe two processes that occur in cells during prophase.

(iii) State the term used to describe the process which occurs after mitosis, when the cell divides into two.

(iv) The diameter of one cell in Figure 7 is 0.075 mm. Which is this diameter in µm?

(b) A student placed a prepared slide on the stage of a light microscope. Describe how to adjust the microscope to view the slide at a magnification of ×400.

(c) Arthritis is a condition that occurs when cells in joints get damaged or destroyed. Stem cell therapy can be used to treat arthritis. Discuss the benefits and risks of using stem cell therapy to treat arthritis.

9 (a) Figure 13 shows a sperm cell.

Figure 13

Describe how structure A and structure B enable fertilisation.

structure A

structure B

(b) Figure 14 shows a human egg cell, magnified ×700.

(Source: © Pascal Goetgheluck / Science Photo Library)

Figure 14

Calculate the actual width of the region indicated by the line on Figure 14. Give your answer in millimetres, in standard form.

* (c) A student investigated the movement of water. Hens’ eggs were placed in vinegar for two days to dissolve the shell. This makes the eggs permeable to water. The eggs were then weighed and placed in different solutions. After 24 hours the eggs were weighed again. Figure 15 shows the results.

Figure 15

Evaluate the results of this investigation. You should include calculations using the data in Figure 15.

Figure 1 shows human blood seen using a light microscope.

The organelle labelled X controls the activities of the white blood cell.

What is the name of organelle X?

Use words from the box to complete the sentences.

Red blood cells contain the substance_........ .

Blood plasma is a_........ .

Describe two ways that white blood cells protect the body from disease.

Figure 2 shows a white blood cell on a 100 µ m scale.

State the width of the white blood cell.

Figure 1 shows human blood seen using a light microscope.

Explain why using an electron microscope shows the structures in the white blood cells more clearly.

In Ireland during the 19th century, a mould caused potato plants to rot.

Explain how this mould affected food security in Ireland.

A group of pupils investigated the effect of temperature on mould growth on bread.

Figure 8 shows the bread after being kept at different temperatures for seven days.

Which is the best estimate of the percentage cover of mould on the bread at 40C?

State two conclusions that can be made about the growth of mould on the bread from 0C to 40C shown in Figure 8.

Explain why there was no mould growing on the bread kept at 60C.

Figure 9 shows some part-baked bread in a sealed bag.

The gas in the bag is nitrogen, which prevents the bread from going mouldy.

If the bag is opened, the bread goes mouldy within days.

State why the bread goes mouldy.

Explain why keeping food in a fridge slows down the growth of mould.

Figure 9 shows the structure and actual size of red blood cells (erythrocytes).

red blood cells side view of red blood cell (cut)

(Source: © N.Vinoth Narasingam/Shutterstock)

Figure 9

Calculate the image size of the top view of this red blood cell if this cell is

Give your answer in mm.

Explain how the shape of a red blood cell is related to its function.

State the role of haemoglobin inside the red blood cell.

Some blood transfusions contain red blood cells.

Red blood cells are stored in a solution containing 5.0% glucose and 0.9% salt.

Explain why red blood cells cannot be stored in pure water.

Between 2013 and 2016 there was an outbreak of a disease called Ebola.

Ebola is estimated to have caused the deaths of more than 11 000 people.

Why is the number of deaths from Ebola only an estimate?

State how Ebola is spread from person to person.

The lytic pathway is part of the lifecycle of the Ebola virus.

After infection of the host cell, components of the virus are produced.

Describe the next stages of the lytic pathway.

The genetic material of a virus can also be inserted into the genome of the host.

Name this type of pathway.

State what is meant by the term genome.

The reaction time of five people was tested using a computer.

These people were then given 100 cm³ of a liquid to drink.

Their reaction times were recorded 10 minutes after drinking the liquid.

Figure 9 shows the results.

Calculate the mean difference in reaction time.

Give your answer in milliseconds.

The drinks manufacturer wants to advertise the effect of the drink on reaction time.

The manufacture needs to confirm the effect on reaction time by improving the investigation.

Give two improvements the manufacturer would need to make to this investigation.

Figure 10 shows a neurone.

Name the type of neurone shown in Figure 10.

Which row identifies structure P and structure Q ?

*(c) Some painkillers prevent neurotransmitters binding to receptors in a synapse.

Explain how a signal is transmitted at a synapse and how the painkillers reduce the pain felt by the person.

James Watson and Francis Crick built a model that showed that DNA has a double helix structure.

Which statement about DNA is correct?

Figure 13 shows the percentage of each base in human DNA.

Describe how this data provides evidence for base pairing in DNA.

A scientist obtained a mass of 0.0062 nanograms of DNA from a diploid human cell.

Calculate the mass of DNA the scientist should obtain from a haploid human cell.

Give your answer in picograms.

(1 nanogram = 1000 picograms)

A student used the method shown in Figure 14 to compare the mass of DNA extracted from strawberry fruit cells and from kiwi fruit cells.

State why ethanol is used.

State two variables the student needs to control when using this method to compare the mass of DNA from these two fruits.

The student repeated the experiment.

Give one reason why.

Mitosis and meiosis are processes that produce new cells.

Compare the outcomes of mitosis and meiosis.

A scientist obtained a mass of 0.0062 nanograms of DNA from a diploid human cell.

Calculate the mass of DNA the scientist should obtain from a haploid human cell.

Give your answer in picograms.

(1 nanogram = 1000 picograms)

A student used the method shown in Figure 3 to compare the mass of DNA extracted from strawberry fruit cells and from kiwi fruit cells.

crush the fruit cells in a buffer solution

filter to separate the soluble DNA from the cell fragments

State why ethanol is used.

State two variables the student needs to control when using this method to compare the mass of DNA from these two fruits.

The student repeated the experiment.

Give one reason why.

Mitosis and meiosis are processes that produce new cells.

Compare the outcomes of mitosis and meiosis.

Organisms can be classified by the five kingdom or three domain method.

What is the name of the domain that plants belong to?

Plant cells contain chloroplasts.

What happens in a chloroplast?

Give a reason why the three domain method of classification has been suggested.

Figure 7 shows a cyanobacterium magnified 50 000 times.

The line AB shows the diameter of the bacterial cell.

(Source: © The Christian Science Monitor)

Figure 7

Calculate the actual diameter of the cyanobacterium.

Give your answer in micrometres (µ m).

Bacterial cells contain plasmids.

Describe three other features of a bacterial cell.

Figure 8 shows a plasmid containing the human insulin gene.

Explain how the human insulin gene can be inserted into a plasmid.

Measles is a disease caused by a virus.

Describe the lytic pathway for a virus.

A measles infection can cause inflammation of the brain.

Figure 11 shows a brain.

Name the part of the brain labelled X.

The death rate from measles is 0.15%.

In 2015, 134 250 people died from measles.

Calculate the number of people infected with measles in 2015.

Give your answer in standard form.

Measles is prevented by immunisation.

State two reasons why people might not be immunised against measles.

The spread of measles is prevented by herd immunity.

Describe herd immunity.

Figure 16 shows the number of neurones in the brain of different animals.

Calculate the difference between the number of neurones in the brain of the rat and the brain of the frog.

Give your answer in standard form.

Most neurones in the brain are unmyelinated whereas motor neurones are myelinated.

Explain why myelination is needed on motor neurones but not on neurones in the brain.

Figure 17 shows a sensory neurone.

Label the axon on Figure 17.

Describe the role of sensory neurones.

Explain how impulses are transmitted at synapses.

(a) Figure 19 shows a diagram of a red blood cell from a turtle and a diagram of a red blood cell from a human.

These cells are animal cells.

Animal cells do not have

The actual length of the red blood cell from a turtle is 20.5 μ m.

Calculate the length of the magnified image of the red blood cell of the turtle when magnified 400 ×.

The width of the human red blood cell, when magnified 400 ×, is 3.08 mm.

Calculate the actual width of the cell and show your answer in standard form.

Red blood cells are carried in veins and arteries.

Figure 20 shows the equipment used to measure the elasticity of an artery.

Describe a method you could use to see how much the ring of tissue from an artery could stretch before it no longer returned to its original size.

Give one safety precaution you need to take when handling animal tissue such as blood vessels.

Figure 21 shows the circulatory system of a frog.

Explain why the circulatory system of a frog is less efficient at carrying oxygen to the tissues than the circulatory system of a human.

Blood is filtered in the kidney to remove unwanted substances.

Figure 1 shows part of a nephron.

Name the structures labelled P and Q.

Figure 2 shows information about some of the components in the blood and in the filtrate in this part of the nephron.

Calculate the difference in the number of red blood cells and the number of white blood cells in 1 cm³ blood.

Give your answer in standard form.

Explain why there are differences in the concentrations of some components in the blood and some components in this part of the nephron.

State the name of the hormone that regulates the water content of the blood.

(a) Figure 3 shows a diagram of a red blood cell from a turtle and a diagram of a red blood cell from a human.

These cells are animal cells.

Animal cells do not have

The actual length of the red blood cell from a turtle is 20.5 μ m.

Calculate the length of the magnified image of the red blood cell of the turtle when magnified 400 ×.

The width of the human red blood cell, when magnified 400 ×, is 3.08 mm.

Calculate the actual width of the cell and show your answer in standard form.

Red blood cells are carried in veins and arteries.

Figure 4 shows the equipment used to measure the elasticity of an artery.

Describe a method you could use to see how much the ring of tissue from an artery could stretch before it no longer returned to its original size.

Give one safety precaution you need to take when handling animal tissue such as blood vessels.