Levels of Organisation

The image below shows a single-celled organism known as Chlamydomonas.

Suggest the group of organisms to which Chlamydomonas belongs.

(1)

Explain your answer to part (i).

(2)

A group of organisms closely related to Chlamydomonas, known as Volvox, forms multicellular structures. Volvox consists of a hollow ball surrounded by an outer layer of cells.

Volvox contains two types of cell:

• Somatic cells which surround the hollow ball to form an outer layer. These cells are unable to divide to produce more cells, but they have flagella which they can use for movement. Somatic cells are similar in structure to Chlamydomonas in part (a).
• Gonidia cells are large cells which are visible as denser regions within the hollow ball. These cells can divide and give rise to new Volvox.

The structure of Volvox is shown in the images below.

Use the information provided to suggest why Volvox is not considered to have tissues or organs.

(2)

Volvox is thought to be a useful model for studying the evolutionary transition between single-celled and multi-cellular organisms.

Suggest why this is the case.

(2)

Some of the structures in kelp can be seen in the diagram below.

Contrast the structural organisation of kelp with that of Volvox in part (b).

Kelp is a type of seaweed, a plant-like organism that gains its food by photosynthesising. Kelp grows by attaching itself to the sea bed with a structure known as a holdfast, allowing the fronds to extend towards the water's surface.

The medulla within the stipe of kelp, shown in part (c), contains cells known as hyphae which transport substances from one part of the kelp to another.

(4)

Name one other group of organisms in which hyphae can be found.

(1)

Separate: Biology Only

Patients with organ failure currently rely on temporary treatments and the use of donor organs for transplant, but scientists believe that it could be possible to improve the treatment for organ failure by growing entire new organs in the lab.

Scientists researching methods that could be used to grow a new heart have been investigating the use of a scaffold developed from the heart of a human or animal donor. A proposed method for this is shown in the image below.

Explain why stem cells are used in this process.

(2)

Suggest why a scaffold is needed for the growth of a new organ in the lab.

(2)

Suggest the practical and ethical considerations that should be taken into account when developing scaffolds from human or animal donors.

(3)

Separate: Biology Only

While growing new hearts for transplant is still some years away, growing skin for transplant from stem cells is currently possible.

A study investigated the effect of stem cells on the rate of healing of skin wounds. Stem cells taken from human skin, known as mesenchymal stem cells (MSC), were administered to skin wounds in immune-deficient mice, and the wounds of the MSC-treated mice were monitored alongside identical wounds in a group of control mice.

The results after 12 days of monitoring are shown below.

Suggest why immune-deficient mice were used in the study.

(1)

Explain the purpose of the control group of mice.

(1)

Calculate the percentage difference in wound healing time between the control group of mice and the MSC-treated mice.

(2)

A student read the results of the study described in part (c) and concluded that MSCs could be used to grow new skin to treat burn patients.

Evaluate the student's conclusion.

The diagram below shows the structure of a ciliated epithelial cell from the airways of a mammal.

Name structures P, Q and R.

(3)

State the function of one other cellular structure that is visible in the diagram.

(1)

The ciliated epithelial cell in part (a) can be found in the lining of the trachea, also known as the windpipe.

Some of the structures associated with the trachea of a mammal are shown in the diagram below.

Note that you are not expected to be familiar with all of these structures.

Use information in the diagram to complete the table below.

The diagram below shows the appearance of the lining of the trachea during an asthma attack.

An asthma attack is inflammation of the airways that occurs in response to an environmental trigger, e.g. smoke or pollen particles in the air.

Use information from part (b) and the diagram above to describe how the cells and tissues of the trachea are changed during an asthma attack.

Suggest how the changes described in part (c) would affect the function of the respiratory system.

The table below contains information about several different organ systems.

Use your knowledge of levels of organisation to complete the table.

Identify the multicellular level of organisation that is missing from the table in part (a).

(1)

Name one example of the level of organisation identified in part (i) found in animals.

(1)

Another example of an organ system is the immune system.

The diagram below shows one of the cells of the immune system, known as a phagocyte. The role of a phagocyte is to engulf and digest pathogens.

Name structures X and Y labelled on the phagocyte.

(2)

Organelle Z is a lysosome, a granule that contains digestive enzymes.

Suggest why phagocytes contain many lysosomes.

(1)

The phagocyte shown in (c) works together with other cells and organs in the immune system to carry out its particular function.

Describe the function of the immune system.