A2.2 Cell structure

Question 1

State the three parts of the cell theory.

Answer 1

1. All living things are composed of cells
2. The cell is the basic unit of life
3. Cells come from pre-existing cells

Question 2

Compare the use of the word theory in daily language and scientific language.

Answer 2

Daily use : a guess there is a doubt

Scientific use : a theory has been shown to be true through repeated observations and experiments. As of yet, no evidence has been collected that contradicts the idea.

Question 3

Distinguish inductive from deductive reasoning.

Answer 3

Inductive reasoning is when you use observations to form a conclusion

Deductive reasoning is when you use knowledge to predict the result

Question 4

Outline the process of inductive reasoning that led to the development of the cell theory.

Answer 4

Inductive reasoning

1. In all the specimen that biologists have seen they have seen one or more cells, therefore all living things are made of cells
2. Subcellular components can’t function whereas full cells have therefore the cell is the most basic unit of life.
3. We have seen cells come from other cells but never seen spontaneous generation, therefore cells come from cells

Question 5

Outline how deductive reasoning can be used to predict characteristics of a newly discovered organism.

Answer 5

Deductive reasoning used the cell theory to predict that slime molds were made of cells.

Question 6

Given the magnification of the ocular and objective lenses, calculate the total microscope magnification.

Answer 6

TOTAL MAGNIFICATION = OCULAR X OBJECTIVE

Question 7

Demonstrate how to focus the microscope on a sample.

Answer 7

Begin with the lowest magnification objective lens, use the coarse focus knob to raise the stage until the sample is in view, and then adjust the fine focus knob for precise focusing. It is important to follow proper safety procedures and handle the microscope carefully throughout the process.

Question 8

Demonstrate how to make a temporary wet mount and stain a microscopic sample.

Answer 8

Place a sample on the slide

Using a pipette, place a drop of water on the specimen

Place the edge of the cover over the sample at an angle and carefully lower the cover slip into place.

If there is too much water, the cover slip will slide around. Place a paper towel and hold it close to the slip to absorb the water

Question 9

Measure the field of view diameter of a microscope under low power.

Answer 9

Place a transparent metric ruler under the low power objective lens to measure the diameter of FOV on low power magnification

Question 10

Calculate the field of view diameter of a microscope under medium or high power.

Answer 10

Use the equation
(Diameter (LP) x Magnification of LP objective )/ Magnification of HP objective

Question 11

Use a formula to calculate the magnification of a micrograph or drawing.

Answer 11

Magnification = size of image / actual size of specimen

Question 12

If given the magnification of a micrograph or drawing, use a formula to calculate the actual size of a specimen.

Answer 12

Estimate the number of the specimen you could fit across the FOV then divide the FOV by that number

Question 13

Compare quantitative and qualitative observations.

Answer 13

The drawings of the cells are qualitative observations where you give cell characteristics whereas the quantitative observation is where you measure the size of specimens or FOV.

Question 14

Define resolution and magnification.

Answer 14

Resolution : the smallest interval distinguishable by the microscope, which then corresponds to the degree of detail visible in an image created by the instrument.

Magnification : how much larger it appears in comparison to real size

Question 15

Compare the functionality of light and electron microscopes.

Answer 15

Light microscopes

Benefits
1. Ease of use
2. Less expensive
3. Can observe dead or living cells in color
4. Cell movement can be studied
5. Quick specimen prep
6. No need for high voltage
Limitations
1. Maximum magnification of about 1500X
2. Low resolving power

Electron microscopes

Benefits
1. Magnification of 100,000 X to 300,000X
2. High resolving power
Limitations
1. Expensive
2. Requires cells to be killed
3. No movement can be seen
4. No color can be seen without stain or dye
5. High voltage required
6. Specimen prep takes a few days

Question 16

Outline the process of visualizing specific proteins in cells using immunofluorescence technology.

Answer 16

Immunofluorescence technology is a technique that uses fluorescently stained antibodies to bind specific target proteins. so that these proteins can be tracked as it moves in a cell.

Question 16

State a benefit of using fluorescent stains to visualize cell structures.

Answer 16

They generate particularly bright images.

Question 17

Outline the process of producing images of cell surfaces using freeze-fracture electron microscopy.

Answer 17

You freeze the sample, fracturing it to reveal cell surfaces, shadowing the fractured surface with a thin layer of metal, and imaging the sample using an electron microscope to capture high-resolution images of the cell surface.

Question 18

Outline the process of visualizing specific proteins using cryogenic electron microscopy.

Answer 18

You flash freeze a sample of protein with vitreous ice, and imaging the sample using an electron or microscope at cryogenic temperatures to obtain high resolution 3D structures of proteins.

Question 19

Outline the function of structures that are common to all cells.

Answer 19

Plasma membrane

• A bilayer formed from phospholipids because they are amphipathic (hydrophilic and hydrophobic regions)
• They are needed to form a wall seperating the cell from the external environment

Cytoplasm

• Cytosol the liquid part of the cytoplasm, is a gel-like fluid substance made of water and many dissolved solutes such as salts, fatty acids, sugars, amino acids, and proteins such as enzymes. These substances are required to carry out metabolic processes

DNA

• Genetic material used by all life forms.

Ribosomes

• catalyzes the synthesis of polypeptides during translation
• Made of two subunits

Question 20

Outline the functions of the following structures of an example prokaryotic cell: cell wall, plasma membrane, cytoplasm, 70s ribosome, and nucleoid DNA.

Answer 20

Cell wall : gives shape and allows the cell to withstand turgor pressure without bursting

Plasma membrane : Regulates what moves into and out of the cell

Cytoplasm : gel like fluid substance, site of metabolic reactions

70s Ribosome : catalyzes the synthesis of polypeptides during translation

Nucleoid DNA : main DNA of the cell

Question 21

Define the term “naked” in relation to prokaryotic DNA.

Answer 21

Prokaryotes are naked when they aren’t associated with proteins.

Question 22

Compare and contrast prokaryotic and eukaryotic cell structure.

Answer 22

Prokaryote
Tiny (0.2-10 micrometer)
No membrane bound organelles
Division by binary fission
Cell wall with peptidoglycan
DNA in nucleoid
Fagella rotates
DNA is circular and naked
Smaller 70’s ribosomes
All unicellular
Essential processes of life
Structures common to all cells
Ribosomes
DNA
Cell membrane
Cytoplasm

Eukaryote
Bigger (10-100 micrometers)
Membrane bound organelles
Division by binary fission, mitosis or meiosis
Cell wall or cellulose or chitin
DNA in nucleus
Fagella moves laterally
DNA is linear and associated with histone proteins
Larger 80’s ribosomes
Multicellular
Essential processes of life
Structures common to all cells
Ribosomes
DNA
Cell membrane
Cytoplasm

Question 23

Outline the function of the following structures in the eukaryotic cell: plasma membrane, cytoplasm, 80s ribosomes, nucleus, mitochondria, chloroplast, endoplasmic reticulum, Golgi apparatus , vesicles, vacuoles, lysosomes, cytoskeleton of microtubules and microfilaments.

Answer 23

Plasma membrane : Regulates what moves into and out of the cell

Cytoplasm : site for metabolic processes

80s ribosomes : catalyzes the synthesis of polypeptides during translation, composed of two subunits. Ribosomes are either floating in the cytoplasm synthesizing polypeptides used in the cell or attached to the endoplasmic reticulum synthesizing polypeptides that are secreted from the cell or become integral proteins in the cell membrane

Nucleus : contains the DNA which stores info for making proteins via transcription and translation, has a double membrane to separate the activities of gene transcription and translation, and contains the nucleolues where ribosome subunits are made

Mitochondria : responsible for the production of ATP. is surrounded by a double cell membrane, they evolved by endosymbiosis

Chloroplast : adapted for photosynthesis, captures light energy and uses it with water and carbon dioxide to produce glucose, they evolved by endosymbiosis

Endoplasmic Reticulum :

RER is a series of connected flattened membranous sacs that play an important role in the synthesis and transport of polypeptides. They also have bound ribosomes to synthesize the polypeptide and release it inside the RER. The RER membrane is continuous with nuclear envelope, which surrounds the cell nucleus.

SER is a series of connected flattened membranous sacs that are continuous with the RER. It lack ribosomes and isn’t involved in protein synthesis. It’s functions are to synthesize phospholids and cholesterorl to repair and form membranes

Golgi apparatus : modifies polypeptides into their functional state. It sorts, concentrates and packs protein into vesicles. Vesicles can be in 1 of 3 destinations : to lysosomes, the plasma membrane, secretion to the outside of the cell

Vesicles : membrane bound sacs that contain and transport materials within cells.

Vacuoles : Maintain the turgor pressure (what keeps the plant upright) against a cell wall. They occupy 30% to 90 % of plant cells area

Lysosomes : small spherical organelles enclosed by a single membrane.

Cytoskeleton : maintains shape of cell organizes cell part and enables cells to move & divide. Composed of microtubules, actin filaments and intermediate filaments

Microtubules : used for intracellular transport of organelles and the separation of chromosomes during mitosis.

Microfilaments : used in various cellular processes such as cell movement, and cell division and cell shape.

Question 24

Define metabolism, homeostasis, excretion, growth, nutrition, movement, reproduction and response to stimuli.

Answer 24

Homeostatis : keep their internal environments stable despite changes in external environment

Metabolism : the sum of all chemical reactions in a cell

Nutrition : all life obtains energy and matter.

Movement : Sessile organisms stay in one place whereas motile organisms are mobile.

Excretion : all organism excrete metabolic waste

Growth : all living things can grow/develop

Response to stimuli : life can respond to changes in environment

Reproduce : all life has the capability of reproduction

Question 24

List the common processes carried out by all life. (8)

Answer 24

Homeostatis, Metabolism, Excretion, Growth, Nutrition, Movement, Reproduction, and Response to stimuli

Question 25

Describe characteristics of Chlamydomonas that enable it to perform the functions of life

Answer 25

photosynthesis for nutrition
detects light and moves to it using flagella - response to stimuli and movement
Grows until it need to divide via mitosis and reproduce asexually
Oxygen is ejected as a biproduct - excretion
Maintains homeostatis by putting excess. water in vacuoles

Question 26

Compare and contrast the structures of plant, animal and fungal cells with reference to cell walls, vacuoles, chloroplasts, centrioles, cilia and flagella.

Answer 26

Chloroplasts are found in plant cells

Cell walls are found in fungi and plant cells

Vacuoles are found in animal, fungi and plant cells

Centrioles are found in plant cells

Cilia and Flagella are found in animal cell, and plant cell

Question 27

Describe features of skeletal muscle fibers that make them an atypical cell.

Answer 27

They have many nuclei

Question 28

Describe features of aseptate fungal hyphae that make them an atypical cell.

Answer 28

They have many nuclei

Question 29

Describe features of red blood cells that make them an atypical cell.

Answer 29

They don’t have a nucleus or a mitochondria

Question 30

Describe features of phloem sieve tube elements that make them an atypical cell.

Answer 30

They have no nucleus and other organelles

Question 31

Compare the number of nuclei in aseptate fungal hyphae, skeletal muscle, red blood cells and phloem sieve tube elements.

Answer 31

Aseptate fungal and skeletal muscle fibers has many nuclei whereas Phloem sieve tube and red blood cells have none.

Question 32

Explain the origin of mitochondria and chloroplast with reference to the endosymbiosis.

Answer 32

Chloroplasts and mitochondria were originally prokaryotic cells and were absorbed by another prokaryotic cell which got bigger by infolding. But instead of being digested they served a function within the cell.

Question 33

Describe the genetic, structural and behavioral evidence for the endosymbiotic theory.

Answer 33

Mitochondria and chloroplasts have the same approximate size, shape and DNA sequences as prokaryotes as well as having a double membrane, 70’s ribosomes, circular naked DNA

They move independently.

Question 34

Outline the benefits of cell specialization in a multicellular organism.

Answer 34

Division of labor.

Question 35

Define differentiation.

Answer 35

The development of specialized structures and functions in cells

Question 36

Describe the relationship between cell differentiation and gene expression.

Answer 36

Gene expression make differentiation of cells possible signalling molecules in the environment activate or repress different transcription factors. which are neccesary to express certain genes in the DNA

Question 37

State that multicellularity has evolved repeatedly.

Answer 37

Multicellularity has evolved repeatedly

Question 38

List groups of organisms that are multicellular.

Answer 38

Animals

Plants

Most fungi

Many algae

Question 39

Outline the steps in the evolution of multicellularity.

Answer 39

Formation of cellular clusters from single cells

Differentiation of the cells within a cluster for specialized functions