Unit 2 Cells

A2.2 cell structure

1. Define unicellular organisms and multicellular organisms.
Some organisms are made of a single cell and are known as unicellular organisms, such as prokaryotes, protists,
and some fungi.
Other organisms are made of many cell and are known as multicellular organisms, such as mammals and
flowering plants.
*Identify the given organisms are categorized into whether eukaryotes or prokaryotes.

2. State the cell theory.

1). All living organisms are composed of cells, which are the smallest unit of life.
2). Cells can only arise from pre-existing cells.
3). Organisms consisting of only one cell carry out all functions of life in that cell.

3. Explain why fungal hyphae are considered as an atypical cell.

It’s made of elongated cytoplasm with multi-nuclei.

4. Explain why skeletal muscle are considered as an atypical cell.

It’s made of large skeletal fibers with multi-nuclei.

5. Explain why red blood cells are considered as an atypical cell.

Atypical cell is a cell that without an organelle normally found in most cells.
The cell theory states that cells are the smallest unit of life and organisms are made of cells.
Red blood cells have no nucleus, but contain hemoglobin to carry oxygen in the blood.
The absence of a nucleus conflicts with cell theory since it differs from the characteristics of typical cells.

6. Sort the following biological materials from the smallest to biggest: cells, organelle, virus, bacteria,
membrane, molecules.
Molecules, membrane, virus, bacteria, organelle, cell.

7. Define resolution.
Resolution is the ability to distinguish two adjacent points or detail in a specimen.

8. Outline the relationships between resolution and magnification.

Resolution is the ability to distinguish two adjacent points or detail in a specimen.
Magnification refers to how much larger an image appears compared to the actual size of the object.
Higher magnification does not necessarily mean better resolution; an image can be magnified but still blurry if
the resolution is low.

9. Calculate the magnification and actual size.

*Magnification = Measured size / Actual size
*cm (*101) mm (*103) nm (*103) µm (*103) um
10. Compare the images collected by electron microscopy and light microscopy.
Light microscopy T.E.M. S.E.M.
Image production Uses light to produce images Uses electron beans to produce images
Maximum magnification x2000 up to x1000000 x200000
Stain used Colored dyes Heavy metals Carbon or gold coating
Specimens that can be viewed Living and non-living Non-living Only non-living
Image created Interior of cell Surface of cell
*Identify the given images are collected by whether Transmission or Scanning electron microscope.

11. State the function of the following microscopy.

Transmission electron microscope Used to view inner structures.
Scanning electron microscope Used to produce an image of the surfaces of structures.
Cryogenic electron microscopy Used to visualize the three-dimensional structure of protein or other
biomolecules.
Freeze fracture electron microscopy Used to visualize the structure of cell membranes.
Fluorescence microscopy Used to specifically locate the target molecules in cells.

13. Draw a labeled diagram to show a typical prokaryotic cell.

14. Outline the functions of the following structures.

Capsule Protection and Attachment.
Cell wall Protection and Maintains the shape of cell.
Cytoplasm Holds organelles and site of some reaction.
Plasma membrane Controls the movements of substances enter and leave the cell.
Ribosome Site of protein synthesis.
Nucleoid Contains genetic materials and control cell activities.
Pili Adherence for attachment pili; Conjugation for sex pili.
Flagella Cell movement.
15. State the name of the process on asexual reproduction and sexual reproduction in bacteria.
Asexual reproduction: Binary fission;
Sexual reproduction: Conjugation.

16. Outline the process of asexual reproduction in bacteria.

DNA replicates which separates into two different areas of the cytoplasm that then divides into two cells.
This process is regarded as binary fission.

17. Draw a labeled diagram to show an active liver cell.

*An active animal cell contains more mitochondria.

18. Draw a labeled diagram to show an typical plant cell.

*An active plant cell contains more chloroplasts.

19. Outline the functions of the following structures.
Nucleolus Ribosomal subunit storage.
Nucleoplasm Genetic materials storage.
rER Site of protein synthesis and modification.
sER Site of lipid synthesis and detoxification.
Golgi apparatus Processes and packages proteins.
Lysosome Digest microbes and unwanted organelle parts.
Mitochondria Site of cellular respiration.
Peroxisome Catalyses breakdown of toxic substances.
Cytoskeleton Provide internal structure and mediate intracellular transport.
Centrosome Organizes spindle microtubules in cell division.
Chloroplast Site of photosynthesis.
Large central vacuole Helps in osmotic balance of cell and storage of substances.

20. State three key features that all typical cells have.
1). Contain DNA as genetic material to control cell activities and need to produce mRNA for proteins
synthesized.
2). Cytoplasm comprised mainly of water, which contains enzyme for catalyzing.
3). Plasma membrane comprised of lipids for semi-permeability and maintains pH.

21. Compare the differences between animals, fungi and plants.

Plant cell Animal cell Fungus cell
Presence of cell wall ✓ ✘ ✓
Composition of cell wall Cellulose / Chitin
Function of vacuoles One, large Many, small Many, small
Presence of chloroplast ✓ ✘ ✘
Presence of centrioles ✘ ✓ ✘
Presence of cilia ✘ Some ✘
Presence of flagella Some Some Some

23. State seven life processes.

Homeostasis, Nutrition, Movement, Excretion, Growth, Response to stimuli, Reproduction.
Supplementary Questions (Based on PPT and Worksheets):
 Explain how different parts of a cell are observed in fluorescence microscopy.
Phosphorescent stains and different type of fluorescence dyes are used to label different parts of n cell that
can be distinguished easily.

 Explain why electron microscopes can see images in greater detail than a light microscope.
Electrons have shorter wavelengths and can distinguish between objects closer together, giving images a high
resolution.

 Which organelle is visible in an electron microscope but not in a light microscope?

A. Nucleus B. Ribosome C. Cell wall D. Golgi Body
*Due to the size of the structures: since ribosomes have smaller size, electron microscope is required in order
to visualize images with higher resolution.

 What could be used to distinguish between a prokaryote and a eukaryote cell?

Size of ribosomes. Prokaryotes contain 70S ribosomes and eukaryotes contain 80S ribosomes.3

 Which organelles are found in large numbers in secretory cells (secrete the products to the outside of a cell)
in animals)? 動物的分泌細胞（將產物分泌到細胞外）中大量存在哪些細胞器？
I. Vesicles II. Gogi Body III. Mitochondria IV. Rough endoplasmic reticulum
All of the above.

 Identify the ultrastructure of eukaryotic cell based on electron micrographs.

 The conformations and functions of the structures in cells.
Prokaryotes
Conformations Functions
Bacterial Is made of polysaccharide layer. Protection and Attachment.
capsule
Cell wall Is made of peptidoglycan. Protection and Maintains the shape of cell.
Plasma Defined as fluid mosaic model. Controls the movements of substances enter
membrane Is comprised of phospholipid, protein, and and leave the cell.
cholesterol.
Cytoplasm Is internal fluid that contains all the enzymes, Holds organelles and site of some reaction.
ribosomes, DNA region.
Ribosomes Is a complex of RNA and protein Site of protein synthesis.
Nucleoid Is the location of circular DNA. Contains genetic materials and control cell
DNA is not associated with histone protein. activities.
Plasmids Contains circular DNA. Conjugation
Pili Is hairlike structure. Adherence for attachment pili; Conjugation
for sex pili.
Flagella Is protein and corkscrew-structure. Cell movement
Eukaryotes
Conformations Functions
Nuclues Is nuclear envelop structure with pores. Nucleoplasm: Genetic materials storage.
Contain nucleolus and DNA region. Nucleolus: Ribosomal subunit storage.
rER System of branching membranes. Site of protein synthesis and modification.
(rER is surrounded by ribosomes.) *Proteins synthesized in rER that are
packaged in vesicles and transport
to golgi body and around the cell.
sER Site of lipid synthesis and detoxification.
Golgi A stack-like collection of flattened Processes and packages proteins.
apparatus membranous sacs.
Lysosome Tiny spherical vesicles bound by a single Digest microbes and unwanted organelle
membrane. parts.
Contains hydrolytic enzymes.
Mitochondria Double membrane structure. Site of cellular respiration.
Inner membrane highly folded into internal
cristae.
Peroxisome Contains catabolic enzymes. Catalyses breakdown of toxic substances.
Cytoskeleton Contain three main types of fibre: Provides internal structure and mediates
microtubules, microfilaments and intermediate intracellular transport.
filament.
Centriole Is nine sets of three microtubules. Organizes spindle microtubules in cell
Centrosome Formed by two centrioles occurred at division.
right-angles.
Chloroplast Double membrane structure. Site of photosynthesis.
Contains thylakoids.
Permanent Is large and central, Fluid-filled internal cavity. Helps in osmotic balance of cell and storage
Vacuole Surrounded by a tonoplast of substances.

 The structure of mitochondria and chloroplast.

 B2.2 organelles and compartmentalization
1. Define organelles and compartmentalization.
An organelle is a ultrastructural unit inside cells, often surrounded by a single or double membrane,
sometimes with no membrane bound.
Compartmentalization refers to the division of a cell into regions or compartments with single or double
membranes between them and cells work much more efficiently than if all reactions were mixed up together.

2. State three types of structures that are not considered as organelles and explain the reasons.
1). Cell wall: that’s because this structure is outside the plasma membrane and the boundary of the cell.
2). Cytoplasm: It has diverse rather that specific functions.
3). Cytoskeleton: that’s because it is not a membrane-bounded structure; it is a network of protein fibers
providing structural support and transport within the cell.

3. Describe the process of cell fractionation and explain how it can be used to study organelles.
Cell fractionation involves homogenizing tissue to break cells open, followed by centrifugation to separate
organelles based on size and density.
Organelles like nuclei are separated at low speeds, while smaller organelles (e.g. ribosomes) require higher
speeds.

4. Why is post-transcriptional modification possible in eukaryotic cells but not in prokaryotic cells?
The eukaryotic cell possesses a nucleus which allows the separation needed for post-transcriptional
modification to occur.
The prokaryotic cell does not have a separating nucleus present to allow this modification.

5. Explain the advantages of compartmentalization in lysosome.

Sealing cellular digestive enzymes in lysosomes, avoids inappropriate autodigestion of other organelles inside
the cell
It can provide an acidic environment for hydrolytic enzymes activation.
It allows the correct concentration of metabolites to present in specific metabolic processes and the
appropriate enzymes to be presented in lysosome.

6. Explain the process of phagocytosis.

Receptors on the plasma membrane recognize the foreign particle and ingested them to form a phagocytic
vacuole.
The vacuole fuses with a lysosome to create a phagolysosome.
The foreign particle is destructed by the enzymes within phagolysosome.
The clathrin proteins help the receptors to bind to specific molecules.
Supplementary Questions (Based on PPT and Worksheets):
 What are the advantages of compartmentalization to the cell?
1). Allows division of labor within the cell, with specific tasks performed by organelles
2). Isolation of incompatible biochemical reactions, e.g., hydrolytic enzymes in lysosomes
3). Creation of specialized microenvironments for efficient enzymatic activity, e.g., high pH for lysosomal
digestion.

 List some examples of single, double, and non-membrane bound organelles.

Single membrane bound: rER, sER, golgi apparatus, vesicle, lysosome, peroxisome, vacuole;
Double membrane bound: nuclues, mitochondria, chloroplast;
Non-membrane bound: ribosome, centrosome.

 What types of substances are most likely to be found in vesicles leaving the sER?
Lipids.
{The role of sER is lipid synthesis, therefore the vesicles transport the lipids produced by sER.}

 Which cell organelle contains structures called cisterna that are involved in the transport and modification
of substances?
Golgi apparatus.

 A mitochondrion within a eukaryotic cell has been damaged. What cell structure will be seen moving
towards it and, eventually, connecting with it.
Lysosomes.

 What is the main advantage of cell compartmentalization in eukaryotic cells?

A. Increase the surface area of the plasma membrane.
B. Allows separation of incompatible biochemical processes.
C. Protects cells from external environmental changes.
D. Provides structural support and rigidity.

 What is an advantage of the separation of the nucleus and cytoplasm into separate compartments in
eukaryotes.
Post-transcriptional modification of mRNA can happen before mRNA meets ribosomes in the cytoplasm.

 What is the main roles of lysosomes in cell compartmentalization?

They isolate hydrolytic enzymes that require an acidic environment.

 Which of the following is true for ribosomes?

A. Ribosomes consist of a large and a small subunit composed of protein and transfer RNA (tRNA).
B. Ribosomes exist in the cells of all living organisms.
{Ribosomes contain rRNA, not tRNA}
 B2.3 cell specialization
1. State the roles of morphogens.
Morphogens are signal molecules that control cell differentiation.
Its concentration controls the initiation or inhibition of gene expression.
It control the way cells differentiate and develop into specific tissues.

2. Define the stem cell.

Stem cell is undifferentiated cell in embryo or adult. It can divide endlessly and differentiate along different
pathways. It’s found in all multicellular organisms.

3. State where embryonic stem cells can be found.

They can found in inner cells in Blastocyst.

4. Define apical meristem and lateral meristem in plant tissue.

Apical meristem: Located at the tips of roots and shoots, responsible for primary growth to increase plant
length.
Lateral meristem: Found along the sides of stems and roots, responsible for secondary growth to increase
plant thickness.

5. Compare the differences between adult and embryonic stem cells.

Adult stem cell Embryonic stem cell
Differentiation Multipotent or pluripotent Totipotent
origins adult tissues Inner cell mass of blastocyst
Main functions Repair and maintainance Development
Immune response Autologous cell mount low immune response Mount an immune response
number and activity Decrease in both as one ages Do not decrease

6. Compare and contrast totipotent, pluripotent and multipotent stem cells.

Totipotent stem cell: only last 4-6 days early in embryo stage; it can produce any tissue in the organisms, also a
complete organism.
Pluripotent stem cell: exist after 4-6 days in embryo stage; it can produce most but not all tissue of organism,
may not produce a complete organism.
Multipotent stem cell: exist after embryo in adult stage; it can produce only a limited number of cell types and
certainly not a complete organism.

7. Define stem cell niches in adult humans and state the role of it.
It’s a specific micro-environment provided within a tissue, where maintain the stem cells or promote
proliferation and differentiation.

8. List two stem cell niches can be found in adult humans.

Bone marrow and hair follicles.
9. Explain how the surface area-to-volume ratio influences cell sizes.
SA refers to the rate of heat and waste exchange.
Volume refers to the heat and waste production.
SA decreases at a slower rate than the volume of a cell.
Cells become too large are not able to bring in enough materials to meet their need due to at low surface area
to volume ratios, exchange of materials takes longer.
Keeping division can keep the cell becomes small.

Supplementary Questions (Based on PPT and Worksheets):

 Discuss the advantages and disadvantages of the use of adult stem cells.
Adult stem cells can divide endlessly.
It can be used to repair tissues.
It has fewer ethical objections than embryonic stem cells.
No rejection problems.
It’s difficult to obtain in adult body.
Adult stem cells differentiate into fewer cell types than embryonic cells.

 For each of the following human cell types, list an adaptation it possesses to carry out its major function:
Red blood cell.
The absence of nucleus and mitochondria allows more space for hemoglobin.
This also creates the biconcave shape, which gives a greater surface area for oxygen absorption.
Hemoglobin can combine with and release oxygen.
It’s flexible and size-limited to allow movement through narrow capillaries.

 Which of the following would not be considered a specialized feature of a differentiated cell?
A. Single nucleus B. Gamete
C. Many nuclei D. Presence of haemoglobin

 What is the primary role of totipotent stem cells in early development?

To differentiate into all cell types, including placental cells.

 What is the main difference between embryonic and adult stem cells?
Embryonic stem cells can differentiate into any cell type, while adult stem cells are limited to certain types.

 Explain why the rate of successful differentiation of embryonic stem cells is higher that adult stem cells’.
That’s because embryonic stem cells is totipotent, which can rise to all types of cells.
However, adult stem cells, such as multipotent and pluripotent cannot rise to some cells, e.g. placental cells.

 Explain the role of bone marrow in human adults as an example of stem cell niches.
It’s the site of blood cell formation. It contains osteoblasts in the niches to regulate the creation of new bone,
and haematopoietic stem cells (HSCs) to produce cellular components of blood and blood plasma.
 Explain the role of hair follicles in human adults as an example of stem cell niches.
It can regenerate to continuously produce new hair.
During growth phase, hair follicles stem cells become activated to regenerate the hair follicle and hair, and
hairs grow longer each day.
During resting phase, stem cells are dormant and hairs can shed more easily.

 What happens to the cell SA:Vol ratio as a cell grows?

It decrease, so rate of gas exchange is too low.
As a cell grows, volume increases faster than surface area, leading to a decreased SA:Vol ratio.
Hence growing cells tend to divide and remain small volume in order to maintain a high SA:Vol ratio suitable
for survival.
When a maximum size is reached, cell growth stops.
The cell may then divide

 SA:Vol ratio calculations:

*SA(surface area): 6*d2; It refers to the rate of heat and waste exchange.
*Vol(volume): d3; It refers to the production of heat and waste.
*SA>Vol  increased SA:Vol ratio  high rate of exchanging materials  division  survive
*Vol>SA  decreased SA: Vol ratio  high waste production  apoptosis  dead

A cube-shaped cell has a side length of 2µm. Calculate the surface area, volume, and the SA:Vol ratio of the
cell. Then explain how this ratio affects the cell’s efficiency in exchanging materials.
SA = 6 * d2 = 6 * 22 = 24µm2
Vol = d3 = 23 = 8µm3
SA:Vol ratio = SA / Vol = 24 / 8 = 3 : 1
Cells with high SA:Vol ratio are more efficient for sufficient transport relative to the cell’s volume.

B2.1 membrane and membrane transport

1. Draw the structure of plasma membrane.