Cells: Theory (DP IB Biology: HL)

A patient with a spinal cord injury was healed using stem cell therapy by the following process:

1. Stem cells collected from the patient's own tissues.
2. Stem cells cultured in laboratory for one month to increase their numbers.
3. Stem cells injected into injury site of patient.
4. Stem cells develop into nerve cells and replace damaged nerve tissue.

Suggest two properties of the stem cells that made this therapy possible.

Explain why the stem cells used in part (a) were taken from the patient and not from a stem cell donor.

Although it would also be possible to use embryonic stem cells from embryos created by IVF to treat the patient in part (a), this is a controversial method. Explain why.

The drawing below shows part of a plant cell as seen with an electron microscope. The scale bar (measuring 45 mm in length) on this drawing represents a length of 10 μm.

Calculate the magnification of the drawing. Show your working.

Calculate the actual width of the cell in part (a) from A to B. Give your answer in micrometres (µm) and show your working.

Identify two ways in which striated muscle fibres (fused muscle cells) differ from the cell shown in part (a). 

Calculate the surface area to volume ratio of a cube with each edge measuring 2 cm. Show your working.

When first hatched, the young tadpoles of some frog species are less than 1.5 mm long and have not yet developed gills.

Explain how these young tadpoles are able to get enough oxygen to their cells without developed gills.

A researcher calculated the surface area of a large number of frog eggs. She calculated the mean surface area to be 10.12 mm². Frog eggs are generally spherical. She calculated the surface area using the following equation: 4πr².

The diagram below is of a mitochondrion at a magnification of ×20 000. The distance between points A and B in the diagram is 6.4 cm.

Calculate the actual length of this mitochondrion in micrometres (µm). Show your working.

The circumference of a mitochondrion, labelled C in the diagram in part (a), is 1.5 µm. A student is making an accurate scale model of a mitochondrion for a school science project and wants to magnify a mitochondrion 50,000 times.

In centimetres (cm), what will be in the circumference of the student’s model?

The mitochondrion in part (a) is responsible for the process of cell respiration to release energy. Which ‘function of life’ is this set of chemical reactions a part of?

Briefly outline the key ideas that make up cell theory.

One mark is available for clarity of communication throughout this question.

Discuss the advantages of the use of adult stem cells.

You are given a sample of plant tissue. Describe how you would prepare and view a sample of cells from this tissue using a light microscope.

Explain why surface area to volume ratio is an important factor in limiting cell size.

Pseudonaja textilis (Eastern Brown Snake) has a group of specialised chemoreceptors located in the Jacobson’s organ, which is on the roof of the snake's mouth. It also has venom glands that produce a neurotoxin.

These are essential in allowing the snake to detect and paralyse its prey.

Explain the property described in this passage that allows multicellular organisms to function efficiently.

The Jacobson’s organ in Pseudonaja textilis (Eastern Brown Snake) is a pair of crescent-shaped chambers where odour molecules are deposited by the forked tongue when it retracts back into the mouth.

Suggest why Jacobson’s organ is crescent-shaped.

Scientists studying the expression of olfactory receptor (OR) genes in four snake species found that fewer than 3% were non-functional genes compared to humans who have up to 67% non-functioning OR genes. These genes code for olfactory receptor proteins located in the cilia of the nostrils.

Deduce why the expression of certain genes, like the OR gene in nostrils, is beneficial to multicellular organisms.

Creutzfeldt-Jakob disease is a rare neurodegenerative disease caused by abnormally-folded proteins found in the brain. Proteins that trigger abnormal folding are called prions.

Suggest why scientists have not classified prions as living.

Viruses and viroids are two other particles that are not considered to be living entities. These are considered exceptions to the cell theory. 

Discuss two other discrepancies to cell theory that scientists have discovered.

Euglena gracilis is a unicellular eukaryotic organism that inhabits moist soils and stagnant fresh water, often forming green scum on the surface of ponds and lakes.

E. gracilis are heterotrophic and autotrophic, and propel themselves using a flagellum. They have an eyespot which allows them to respond to sunlight and contractile vacuoles that regulate the composition of the cytoplasm.

Compare the functions of life of E.gracilis and a Paramecium species.

A plant palisade mesophyll cell is 4 μm in width and depth, and 25 μm in length.

Its shape is approximately cuboid. 

Calculate the surface area to volume ratio of this cell. Show your working.

If the palisade cell in part (a) has a large central vacuole, so that the cytoplasm (not including the vacuole) extends inward 500 nm from the plasma membrane of the cell. 
    
Calculate the surface area to cytoplasmic volume ratio. Show your working.

From part (b) comment on what the function of the plant vacuole is. 

The image below is a photomicrograph of a transverse section through part of a stem.

Doc. RNDr. Josef Reischig, CSc., CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Draw a large tissue plan diagram of this part of the stem.

A student used a light microscope to study the plant stem pictured in part (a). The diagram below shows the stage micrometer scale that was used to calibrate an eyepiece graticule. 

One division, on either the stage micrometer scale or the eyepiece graticule, is the distance between two adjacent lines. 

The length of one division on this stage micrometer is 0.01 mm.

Using this stage micrometer, calculate the actual length of one eyepiece graticule division. Show your work.

The photomicrograph below was taken using the same microscope with the same lenses as part (b).

The same eyepiece graticule was also used; a section of that graticule is shown under the image below.

Use the calibration of the eyepiece graticule unit from part (b) and the information in the photomicrograph to estimate the actual length in μm of the plant tissue from A to B. 

Explain the importance of the surface area to volume ratio to a growing bacterial cell.

Evaluate two named therapeutic uses of stem cells.

Compare and contrast the functions of life in a Paramecium with a named photosynthesising organism.