Theme A: A2 Cells - A2.2 Cell Structure

Question 1

3 main points of the cell theory

Answer 1

1) all organisms are composed of one or more cells
2) cells are the smallest unit of life
3) all cells come from pre-existing cells

Question 2

main subunits in scientific notation

Answer 2

1 m (100 cm or 1,000 mm)
1 cm = x10^-2m (0.01 m)
1 mm = x10^-3m (0.001 m)
1 µm = x10^-6m (0.000001 m)
1 nm = x10^-9m (0.000000001 m)

Question 3

magnification

Answer 3

the increase in an objects image size compared to its actual size.
magnification = measured size of the image / actual size of the specimen
* make sure to convert the sizes so that they have the same unit

Question 4

resolution

Answer 4

the minimal distance between 2 points or objects at which they can still be distinguished. as microscope resolution improves, it reveals images with greater detail and clarity

Question 5

compare a light microscope and an electron microscopes (EM)

Answer 5

light microscope
1) inexpensive to buy and operate
2) simple and easy to prepare specimens
3) magnifies up to x2,000
4) specimens can be living or dead

electron microscopes
1) expensive to buy and operate
2) complex and length specimen preparation
3) magnifies over x500,000
4) specimens must be dead and typically fixed in a material like plastic

Question 6

size of biological structures from largest to smallest

Answer 6

cells –> organelles –> bacteria –> viruses –> membranes –> molecules

Question 7

field of vision (view)

Answer 7

total visible area when looking through a microscope’s ocular/eye piece. its diameter is calculated using special micrometers

Question 8

types of micrometers

Answer 8

1) ocular micrometer (“graticule”)
2) stage micrometer

Question 9

ocular micrometer (“graticule”) and stage micrometer

Answer 9

The ocular micrometer, located in the eye piece, is a glass disc engraved with equally spaced, arbitrary units. These units do not correspond to any specific measurement by themselves. The ocular micrometer is calibrated using a stage micrometer, which is a microscope slide with a precisely engraved scale, usually marked in millimeters or micrometers. By comparing the two, you can determine the actual size of the object under examination

Question 10

objective power

Answer 10

the magnification provided by the objective lens

Question 11

scanning electron microscope (SEM)

Answer 11

aims a beam of electrons to scan the surface of specimens

Question 12

transmission electron microscope (TEM)

Answer 12

uses a beam of electrons to scan the surface of a specimen

Question 13

freeze fracture

Answer 13

A preparation technique for electron microscopy in which a specimen is rapidly frozen using liquid nitrogen and then physically broken apart (fractured) in a vacuum. It can be used to provide a planar view of the internal organisation of cell membranes.

Question 14

cryogenic electron microscopy

Answer 14

This involves flash-freezing solutions containing proteins or other biological molecules. The frozen solution is then exposed to electrons to produce images of individual molecules. Computer software is used to provide the 3D framework of a cell’s proteins using the images of individual molecules.

Question 15

disadvantages of electron microscopes

Answer 15

1) expensive
2) require expensive training to operate
3) involves dead specimens embedded in a kind of matrix - like plastic
4) The lengthy treatment required to prepare specimens means that artefacts can be introduced. Artefacts look like real structures in the cell, but are actually the results of preserving and staining

Question 16

fluorescent stains

Answer 16

this preparation technique used with light microscopes involves dyes that combine with specific cellular components. the parts of the living cell that accept the dye will fluoresce when irradiated with ultraviolet or violet-blue light, giving a more detailed view of the specimen

Question 17

immunofluorescence

Answer 17

this technique - use in light microscopy - involves the use of antibodies that have been prepared with fluorescent dyes which can bind with target molecules complimentary to the antibody. This allows specific molecules to be detected, where viral proteins are often the target

Question 18

condenser

Answer 18

located between stage and light source. it has a lens that directs light rays from the light source through the specimen. the rays then pass through the objective lens to the ocular lens which is where the image is viewed

Question 19

common structures that all cells possess

Answer 19

1) DNA
2) cytoplasm
3) plasma membrane

Question 20

DNA

Answer 20

• DNA stores and transfers genetic information by forming large molecules from nucleotides.
• 4 different nucleotides make up DNA and the sequence of these nucleotides determines the production of specific proteins, which are essential for passing on traits from cell to cell.

Question 21

cytoplasm

Answer 21

• cytoplasm is the internal fluid of a cell. it consists of the cytosol (a water-based matrix) and the cell’s organelles.
• the cytosol is mostly made up of water, but it also contains the ingredients necessary to conduct its daily activities.
• most metabolic reactions occur within the cytoplasm

Question 22

general function and structure of a cell membrane (plasma membrane)

Answer 22

• the cell membrane (plasma membrane) is a selectively permeable barrier that protects the interior of the cell from its external environment.
• it is composed of a phospholipid bilayer with embedded proteins
• it controls the movement of substances in and out of the cell, allowing necessary materials to enter and waste to exit
• CREATE DISTINCT PARTS OF THE CELL (COMPARTMENTALISATION)

Question 23

types of prokaryotic cells

Answer 23

bacteria and archae

Question 24

features of a prokaryotic cell

Answer 24

in all prokaryotes…
1) cell wall
2) plasma membrane
3) ribosomes
4) nucleoid region

in some prokaryotes…
5) pili
6) flagella
7) capsule
8) plasmid

Question 25

cell wall (prokaryote)

Answer 25

• protects and maintains the shape of a cell
• prevents the cell from rupturing when water pressure greater inside the of cell than its surroundings
• it’s made of a carbohydrate-protein complex called peptidoglycan

Question 26

gram staining

Answer 26

• Bacteria are classified via gram staining
• gram positive bacteria have a thick peptidoglycan layer in their cell wall that take on a blue or violet appearance when exposed to a dye called crystal violet
• Gram-negative bacteria have a thinner peptidoglycan layer but also have an additional outer membrane. The outer membrane is dissolved by alcohol during the staining process, allowing the crystal violet dye to wash out

Question 27

capsule

Answer 27

• some bacteria have an additional layer of polysaccharide outside of its cell wall
• it allows the bacterium to adhere to structures such as teeth, skin, food, etc.

Question 28

plasma membrane (prokaryotes)

Answer 28

• located just inside the cell wall
• prokaryotes have a similar plasma membrane to eukaryotes except they often have more complex roles especially in multicellular organisms
• controls the movement of material in and out of the cell and plays a role in binary fission

Question 29

pili

Answer 29

• some bacteria contain hair-like growths one the outside of their cell wall
• it can be used to attach the bacterium to structures like teeth and skin
• its main function is joining bacterial cells in preparation for the transfer of DNA from one cell to another, which is also known as asexual reproduction

Question 30

flagella

Answer 30

• some prokaryotic cells have flagella (plural) or a flagellum (singular) that are always longer than the pili
• it allows the cell to move
• flagella are anchored to the cell’s cell wall and plasma membrane

Question 31

cytoplasm (prokaryotes)

Answer 31

• occupies the complete interior of the cell
• there are no specialised areas within the cytoplasm as no internal membrane exist in prokaryotic cells
• this is where are all cellular processes take place

Question 32

ribosomes

Answer 32

• always composed of protein and ribosomal RNA (rRNA)
• they function as sites of protein synthesis
• ribosomes are composed of 2 sub units: in prokaryotic cells, the 2 subunits equal 70S (thus they contain 70S ribosomes), in eukaryotic cells, the 2 subunits equal 80S making them larger and denser
• ribosomes may be found free floating in the cytoplasm or they may be attached to the surface of ER

Question 33

nucleoid region

Answer 33

• the nucleoid region is non-compartmentalised meaning it is not surrounded by a membrane
• it contains a single, long, circular thread of DNA known as the bacterial chromosome
• prokaryotic cell DNA is not associated with histones and so bacterial chromosomes are described as naked loops
• the nucleoid region is involved with cell control and reproduction

Question 34

plasmid

Answer 34

• some prokaryotes contain plasmids which are small, circular DNA molecules that are disconnected from the main bacterial chromosome and replicate independently
• prokaryotic cells do not require plasmid DNA under normal conditions, but it can help the cell adapt to unusual circumstances

Question 35

binary fission

Answer 35

Definition: The process by which prokaryotic cells divide, resulting in two genetically identical daughter cells.
Steps:
1) The DNA is replicated, producing two identical daughter chromosomes.
2) Each daughter chromosome attaches to a different region of the plasma membrane.
3) The cell elongates, and specialised protein fibres help partition the replicated DNA.
4) The plasma membrane pinches inwards, and the cell divides, forming two genetically identical daughter cells.

Question 36

types of eukaryotic cells

Answer 36

algae, protozoa, fungi, plants, and animals

Question 37

organelles

Answer 37

Organelles are specialized structures within a cell that perform distinct functions necessary for cellular operation

Question 38

compartmentalisation

Answer 38

enables different chemical reactions to be separated, which is especially important when adjacent reactions are incompatible. it also allows chemicals for specific reactions to be isolated; this isolation results in increased efficiency.

Question 39

organelles of eukaryotic cells

Answer 39

1) endoplasmic reticulum
2) ribosomes
3) lysosomes
4) Golgi apparatus
5) mitochondria
6) nucleus
7) chloroplasts
8) centrosomes (centrioles)
9) vacuoles

Question 40

cytoplasm (eukaryotes) + cytoskeleton

Answer 40

• eukaryotic cytoplasm includes a cytoskeleton
• the cytoskeleton is a dynamic network of protein fibres in the cytoplasm. these fibres can rearrange their protein components so the cell can respond to changes in internal and external environments.
• it is composed of:
  1) microfilaments (actin filaments): involved in cell division and cell movement.
  2) microtubules: shape and support the cell, as well as provide tracks for organelle movement.
  3) intermediate filaments: reinforce cell shape and anchor some organelles.

Question 41

endoplasmic reticulum (ER)

Answer 41

• a network of membrane-bound tubules in eukaryotic cells involved in the synthesis, folding, and transport of proteins and lipids
• rough ER has ribosomes on its exterior; synthesises and folds proteins destined for membranes, secretion, or lysosomes (located closer to nuclear membrane)
• smooth ER lacks ribosomes; synthesises lipids, metabolises carbohydrates, and detoxifies drugs and poisons

Question 42

lysosomes

Answer 42

• definition: intracellular digestive centres that arise from the Golgi apparatus
• structure: lysosomes are membrane-bound vesicles containing about 40 hydrolytic enzymes, which break down large molecules using water (hydrolysis)
• function:
  1) maintain acidic conditions necessary for enzyme activity.
  2) break down proteins, nucleic acids, lipids, and carbohydrates by fusing with old or damaged organelles.
  I3) involved in phagocytosis, where they digest materials engulfed by the cell.

Question 43

Golgi apparatus

Answer 43

• it consists of flattened sacs known as cisternae stacked on top of one another
• it functions in the collection, packaging, modification, and distribution of materials synthesised in the cell
• products of the rough ER are received on the cis side nearest to it. the products move into the cisternae and are then discharged one the opposite side called the trans side
• vesicles, like lysosomes, are seen coming from the trans side which carry modified materials to wherever needed in or out of the cell

Question 44

mitochondria

Answer 44

• Size: Similar in size to a bacterial cell.
• Genetic Material: Contains its own circular DNA and produces its own 70S ribosomes, allowing some independence from the cell.
• Structure: Surrounded by two membranes: a smooth outer membrane and an inner membrane folded into cristae. The cristae increase the surface area for chemical reactions.
• Function: The primary site of ATP production through aerobic respiration, providing usable energy for the cell.

Question 45

nucleus

Answer 45

• structure: It is surrounded by a double membrane called the nuclear envelope, which has pores to allow the exchange of materials between the nucleus and the cytoplasm.
• function: the nucleus contains the cell’s genetic material (DNA). It regulates gene expression and controls the cell’s growth, metabolism, and reproduction by coordinating the activities of RNA and protein synthesis.
• exceptions: most have a single nuclei, some have multiple while others have none. cells without a nucleus can’t reproduce, where the loss of reproductive ability allows increased specialisation to carry out other functions

Question 46

nucleoli

Answer 46

most nucleus have a nucleoli where ribosomes are manufactured

Question 47

chloroplasts

Answer 47

• found only in plant and algae cells.
• have a double membrane and are roughly the size of a bacterium.
• contain their own circular DNA and 70S ribosomes (similar to prokaryotes).
• internal structure includes thylakoids, which are flattened membrane sacs containing chlorophyll (the pigment that absorbs light for photosynthesis).
• thylakoids are organised into stacks called grana, surrounded by a fluid-filled matrix called the stroma.
• site of photosynthesis: chloroplasts convert light energy into chemical energy (glucose) during the process of photosynthesis.
• reproduce independently of the cell

Question 48

centrosomes

Answer 48

• location: close to the nucleus in animal cells.
• structure/function: animal cells typically have a pair of centrioles, positioned at right angles to each other. These centrioles are part of the centrosome and play a key role in assembling microtubules, which are essential for maintaining cell structure, intracellular transport, and chromosome movement during cell division (mitosis and meiosis).
• plant and fungal cells lack centrioles but still organise microtubules from centrosome-like regions.
• in cells with cilia or flagella, centrioles form basal bodies, which are found at the base of cilia and flagella and are essential for their formation

Question 49

vacuoles

Answer 49

• vacuoles are membrane-bound organelles that store various substances such as nutrients, metabolic waste, toxins, and water.
• in plant cells, they allow an uptake of water, which provides rigidity to the plant.
• plant cells typically have a large central vacuole, while animal cells contain smaller, more numerous vacuoles.
• vacuoles can be formed from the Golgi apparatus, endoplasmic reticulum, or fusion of vesicles.

Question 50

differences between prokaryotic cells and eukaryotic cells

Answer 50

Prokaryotic cells:
1) DNA is circular and naked (not associated with histone proteins).
2) DNA is free in the cytoplasm (in the nucleoid region, no true nucleus).
3) No mitochondria (energy production occurs in the plasma membrane).
4) 70S ribosomes.
5) No internal compartmentalisation or membrane-bound organelles.
6) Cell size typically less than 10 micrometers.

Eukaryotic Cells:
1) DNA is linear and associated with histone proteins (organised into chromosomes during division).
2) DNA is enclosed within a nuclear envelope (true nucleus present).
3) Mitochondria present (site of aerobic respiration).
4) 80S ribosomes.
5) Internal compartmentalisation is present, with many membrane-bound organelles (e.g., ER, Golgi apparatus).
6) Cell size generally more than 10 micrometers.

Question 51

similarities between prokaryotic cells and eukaryotic cells

Answer 51

1) both have outside boundary that always involve a plasma membrane
2) both conduct all functions of life
3) DNA in both cell types

Question 52

functions of life

Answer 52

1) metabolism: the sum of all the chemical reactions that occur within an organism
2) growth: the development of an organism
3) reproduction: the ability to produce an offspring
4) response to stimuli: as the environment changes, the organism adapts
5) homeostasis: maintenance of a constant internal environment
6) nutrition: ability to acquire the energy and materials needed to maintain life
7) excretion: ability to release material snot needed or harmful into the surrounding environment
8) movement: ability to move or change position

Question 53

similarities between the 3 main eukaryotic cells

Answer 53

1) all contain mitochondria that possess cristae, a matrix, and a double membrane
2) mitochondria functions to produce ATP for cell use in all 3 types

Question 54

differences between the 3 main eukaryotic cells

Answer 54

plant cells:
1) exterior of cell includes an outer cell wall made of cellulose, with a plasma membrane
2) chloroplasts in the cytoplasm enable the production of carbohydrates
3) large central vacuole to store carbohydrates
4) stores carbohydrates as starch
5) usually no flagella, cilia, or basal bodies
6) fixed and often angular shape due to rigid cell wall
7) has centrosomes but no centrioles

animal cells:
1) exterior includes a plasma membrane but no cell wall
2) no chloroplasts for carbohydrate production
3) generally small and numerous vacuoles with many unique functions
4) stores carbohydrates as glycogen
5) may have cilia or flagella associated with basal bodies
6) no cell wall, and so has a flexible and more likely round shape
7) has both centrosomes and centrioles

fungal cells:
1) exterior includes an outer cell wall made of chitin with a plasma membrane
2) same as in animal cell
3) same as in animal cell
4) same as in animal cell
5) may have cilia or flagella but don’t have basal bodies
6) the cell shape may vary, where cell wall allows support and a degree of flexibility
7) same as in plant cell

Question 55

atypical eukaryotes (due to no. nucleus)

Answer 55

1) hyphae: a structure often found in fungal cells that consists of chains separated by cross-walls with pores to allow various organelles and cytoplasm to flow from cell to cell. hyphae without cell walls have multiple nuclei
2) phloem sieve tube: allows transportation within a multicellular plant. they have end walls with pores and minimal cellular components including nuclei, ribosomes, cytoplasm, cytoskeleton. they can only remain alive with companion cells.
3) red blood cells: specialised function of carrying oxygen throughout the body, they contain haemoglobin which easily combines with oxygen. it has no nucleus which allows more room for oxygen
4) skeletal muscle: specialised in body movement. limited presence of cell membranes, resulting in large tubular cells with multiple nuclei, allowing more protein.

Question 56

key points of endosymbiotic theory

Answer 56

1) around 2 billion years ago, a larger eukaryotic cell (with a nucleus) engulfed a smaller prokaryotic cell capable of aerobic respiration.
2) the two cells developed a mutually beneficial (symbiotic) relationship, where the larger cell provided protection, and the smaller cell produced energy (ATP).
3) over time, the smaller cell evolved into a mitochondrion, becoming an integral part of the larger cell’s structure.

Question 57

characteristics of mitochondria as evidence of endosymbiotic theory

Answer 57

its properties are similar to prokaryotic cells:
* similar size to most bacterial cells
* divide independently of host cell by binary fission
* produces its own protein with their own 70S ribosomes
* it has its own DNA in a circular ring
* they have 2 membranes, where the outer membrane is similar to that of eukaryotes, and its inner membrane is like that of prokaryotes. this is consistent with the engulfing process
* the RNA in mitochondrial ribosomes closely resemble the RNA in prokaryotic ribosomes
* the DNA of mitochondria in eukaryotes is more similar to bacteria than the eukaryotic cell, where its believed that the more DNA 2 organisms have in common, the more closely related they are to one another

Question 58

process of cell differentiation in multicellular organisms

Answer 58

Cell differentiation is controlled by the activation / expression of a selection of genes.
Cells which become different in this way have a different pattern of gene expression.
The (expressed) genes cause production of proteins.
The proteins carry out specific functions.
These function give rise to specialised cells that form tissues (in multicellular organisms).

Question 59

cell differentiation

Answer 59

Cell differentiation is the process by which cells become specialised to perform specific functions in an organism