Chapter 2 - Membranes & Cell Organelles – Answers
2 Analysing information and drawing conclusions
Figure 2.29 is a coloured transmission electron micrograph of a plasma cell. One function of plasma cells is to secrete antibodies during an immune response. Note the extensive network of endoplasmic reticulum.
a Explain whether you would expect the ER to be rough or smooth.
b Given the function of plasma cells, what other organelle would you expect to be rather prominent in parts of this cell?
c What is the darkly stained material in the nucleus?
Checklist
Read chapter 2 (pp. 46–8).
Comments
a Rough endoplasmic reticulum rather than smooth endoplasmic reticulum. Ribosomes of rough endoplasmic reticulum are sites of synthesis of proteins for export from cells; in this case those proteins are antibodies.
b Golgi complex because its function is to package proteins for export from the cell
c RNA molecules in the nucleolus
3 Making connections between concepts
Mitochondria and chloroplasts both contain circular molecules of DNA and free ribosomes. What conclusions can reasonably be made on the basis of the presence of such structures?
Checklist
Refer to ‘Odd fact’ (p. 44) and read the section ‘Plant cell organelle: chloroplasts sunlight trappers’ (p. 50).
Comments
The DNA and free ribosomes suggest that mitochondria and chloroplasts may have originated as simple organisms like bacteria that later formed mutually beneficial associations with larger cells.
4 Applying knowledge and understanding
Examine table 2.2 on page 38.
a What is the difference in structure between rough and smooth endoplasmic reticulum?
b Which kind of cell shown in the table has the greater percentage of rough endoplasmic reticulum? Which has the greater percentage of smooth endoplasmicreticulum?
c As a result of this difference, what would you conclude about the fate of the majority of protein produced by each cell? Explain your conclusion.
Checklist
Refer to table 2.2 (p. 38).
Comments
a Rough endoplasmic reticulum (rough ER) consists of membranes that form the walls of channels or passageways through the cytoplasm and ribosomes on the outside of the walls. Smooth ER consists of the membranes only, without the attached ribosomes.
b The pancreatic cell has greater percentage of rough ER. The liver cell has a greater percentage of smooth ER.
c Based on the answer to (b), the pancreatic cell produces more proteins for export from the cell while the liver cell produces more proteins for use within the cell.
5 Analysing information and drawing conclusions
The folded internal membranes of mitochondria have many stalked particles on their innermost surfaces (see figure 2.30). Given the function of mitochondria and where most of the reactions occur, of what advantage might the presence of these particles be for the production of ATP in the organelle?
Checklist
Read the section ‘Organelle 2: mitochondrion energy-supplying organelle’
(p. 44) and apply general principles relevant to biology.
Comments
The presence of the stalked particles on the inner membrane of the mitochondrion would increase the surface area of the inner membrane and therefore presumably it would provide more area for ATP production.
6 Analysing information and drawing conclusions
In figure 2.30, you may have noted the holes in the folds of the inner membrane of mitochondria. Explain a possible function for these holes.
Checklist
Read the section ‘Mitochondrion’ (p. 44) and apply general principles relevant to biology.
Comments
The holes in the folds of the inner membrane of the mitochondrion may perhaps provide a passage for large molecules to move through, rather than around, the inner membrane. Maybe their function is something entirely different. You may suggest another function based on your understanding of general biological principles.
7 Applying knowledge and understanding
Examine figure 2.31, which is a coloured, high-resolution scanning electron micrograph of a portion of cell.
a Explain whether you can distinguish if the cell involved came from an animal or a plant.
b What is the name of the structure shown?
c What is its function?
Checklist
Read pp. 39–50 and refer to figure 2.23 (p. 51).
Comments
a It is not possible to decide whether this cell portion is from a plant cell or an animal cell because the image does not show any feature, such as a cell wall
or chloroplast, that would distinguish a plant cell from an animal cell.
b Golgi complex
c Its function is to package proteins for export (secretion) from the cell.
8 Analysing information and drawing conclusions _ Figure 2.32 shows a portion of an animal cell.
a From what part of the cell has the structure been taken?
b Name the kind of organic molecule labelled X, Y and Z.
c Explain the function of the structure labelled W.
Checklist
Read the section ‘The plasma membrane boundary’ (pp. 39-42).
Comments
a Plasma membrane
b Organic molecules are: X protein; Y carbohydrate; Z phospholipid.
c The function of W, which is a protein-lined pore or channel through the membrane, is to allow for the movement of hydrophilic molecules and ions across the membrane.
9 Analysing information and applying knowledge and understanding
Fats are generally transported in the blood in the form of small particles, called chylomicrons. Examine the three examples given in figure 2.33. Note the compounds that make up these particles. Explain why the components of the particles aggregate in the way they do, ending up as spherical.
Checklist
Refer to chapter 1 ‘The chemical nature of cells’ (p. 2).
Comments
The molecules within these complexes aggregate as they do because of the interaction of the molecules within them with water. Hydrophilic molecules or portions of them interact with water molecules and therefore face outwards from the surface of the sphere. Enclosed within the sphere are lipid molecules that do not interact with water but interact with themselves; they are lipophilic.
10 Applying knowledge and understanding
Examine figure 2.34 which shows a coloured scanning electron micrograph of a portion of cell.
a Name structure X and state its function.
b Given the density of the X structures, what could you reasonably deduce about the metabolic rate of this cell?
c Name structure Y and state its function.
Checklist
Read the sections ‘Organelle 2: mitochondrion’ (p. 44), ‘Organelle 3: ribosomes
— protein factories’ (p. 45) and ‘Organelles 4 and 5: endoplasmic reticulum and Golgi complex’ (pp. 46-48).
Comments
a X is a mitochondrion. Its function is the production of ATP
b A high metabolic rate because it requires a lot of energy (ATP) to function
c Y is rough endoplasmic reticulum. Its function is the synthesis of proteins which will be exported (secreted) from the cell.
11 Using the web
Go to www.jaconline.com.au/natureofbiology/natbiol2-3e and click on the ‘Cytoskeleton’ weblink for this chapter. Select ‘Cell biology’ at the left-hand side. Scroll down and click on ‘The cytoskeleton’. Then select ‘Microtubules, microfilaments and intermediate filaments’.
a What is the role of the cytoskeleton?
b i What is the main protein found in microfilaments? Name two properties of this protein.
ii Which protein is associated with muscle contraction?
c i Which protein is found in microtubules?
ii Name two functions of microtubules.
Checklist
Read the section ‘The cell skeleton’ (p. 52).
Comments
a The role of the cytoskeleton is to provide movement and stability (strength and support).
b i The main protein in microfilaments is actin, but some microfilaments in muscle cells consist of the protein myosin.
ii Actin has the capacity to shorten. (In skeletal muscle especially it is the interaction between actin and myosin molecules (microfilaments) that results in skeletal muscle fibres shortening.)
c i Microtubules consist of the protein tubulin.
ii One function of tubulin is to cause chromosomes to move towards the poles of cells during cell division.
12 Using the web
Go to www.jaconline.com.au/natureofbiology/natbiol2-3e and click on the ‘Cell structure animation’ weblink for this chapter. Select the option ‘Cell Structure’.
a Explore the animations to test your knowledge and understanding of the structural characteristics of prokaryotic, animal and plant cells.
b Design two cells, one animal and one plant. Use these two designed cells to test the knowledge of your biology practical work partner.
Checklist
Answers can be written after reading all of chapter 2.
Comments
a These animations show prokaryotic cells and compare them to eukaryotic cells; compare plant cells with animal cells; and explore the functions of the different organelles within eukaryotic cells.
b Students will need to know features that would distinguish a plant cell from an animal cell, e.g. cell wall, plasmodesmata, chloroplasts, large vacuole.
BIOCHALLENGE (p. 56)
1. a A nuclear pore; B nuclear membrane; C nucleolus; D nucleus
b cytosol
c RNA molecules
d free in the cytoplasm and attached to endoplasmic reticulum forming rough ER
2. a plant cell
b A ribosomes; B smooth endoplasmic reticulum; C cell wall; D Golgi complex
(Golgi apparatus); E microfilament; F plasmodesma (singular; plasmodesmata plural)
c to allow movement of small molecules and ions between cytoplasm of adjacent cells
d Plasmodesmata allow small molecules to pass between cells. These junctions allow communication between adjacent cells.
3. a A plasma membrane; B secretory vesicle
b Golgi complex. The function of the complex is to package protein in secretory vesicles.
c The different images are due to the structure being viewed from different perspectives (e.g. side view compared with top-down view).