A2.2 cell structure

Question 1

Cytology

Answer 1

Cytology is the branch of biology that studies all facets of the cell.

As our understanding of the cell has increased, so has our ability to understand all forms of life and diseases that occur on planet Earth.

Question 2

units and their measurement

Answer 2

1 metre (m) (100 cm = 1,000 mm)
1 centimetre (cm) (0.01 m)
1 millimetre (mm) (0.001 m)
1 micrometre (um) (0.000001 m)
1 nanometre (nm) (0.000000001 m)

Question 3

What is magnification in microscopy?

Answer 3

Magnification refers to the increase in an object’s image size compared to its actual size.

It’s represented in numbers like 500× or 100,000×, indicating how much larger the image is than the actual object.

Question 4

Define resolution in microscopy.

Answer 4

Resolution is the minimal distance between two distinguishable points or objects. Higher resolution microscopes reveal greater detail, often compared to clarity, with increased resolution providing clearer images.

Question 5

How do light microscopes operate, and what do they use to enhance visibility?

Answer 5

Light microscopes use light to pass through specimens, living or dead, to form an image. Stains might be applied to improve the visibility of structures within the specimen.

Question 6

What distinguishes electron microscopes (EMs) from light microscopes?

Answer 6

Electron microscopes provide the highest magnification (over 100,000×) and resolution. They use electron beams passing through specimens to form images, enabling ultra-high magnification and detailed views.

Question 7

Light microscope

Answer 7

Inexpensive to purchase and operate
Simple and easy specimen preparation
Magnifies up to 2,000×

Question 8

Electron microscope

Answer 8

Expensive to purchase and operate
Complex and lengthy specimen preparation
Magnifies over 500,000x

Question 9

What is the order of sizes from largest to smallest, in terms of cells and their components?

Answer 9

Cells > Organelles > Bacteria (some similar in size to organelles) > Viruses > Membranes > Molecules.

Question 10

What is the field of view in a microscope, and how is its diameter calculated?

Answer 10

The field of view is the total visible area through a microscope’s ocular or eyepiece. Its diameter is calculated using specialized micrometers, such as ocular and stage micrometers.

Question 11

What is an ocular micrometer, and how is it calibrated?

Answer 11

The ocular micrometer, located in the eyepiece, is engraved with equal units, but these units are arbitrary. Calibration is done using a stage micrometer with defined units, typically calibrated with a ruler or a special slide with known units (usually millimeters).

Question 12

How is the magnification of a specimen calculated using a microscope?

Answer 12

Measured size of image / Actual size of specimen = Magnification.

Question 13

What significant advancements have been made in microscopy since Robert Hooke’s microscope in 1665?

Answer 13

Electron microscopy, including techniques like freeze fracture and cryogenic electron microscopy, has significantly progressed since early microscopes.

Question 14

What distinguishes an electron microscope (EM) from a light microscope in terms of its operating principle?

Answer 14

EMs use a beam of electrons, which have a shorter wavelength than light, providing over a 1,000 times greater resolving power and magnification up to 500,000× compared to a light microscope’s maximum of 2,000×.

Question 15

What are the two types of electron microscopes and how do they differ?

Answer 15

Scanning electron microscopes (SEM) scan a specimen’s surface with an electron beam, while transmission electron microscopes (TEM) pass electrons through thin sections for internal structure examination.

Question 16

What are the techniques employed in electron microscopy and their contributions?

Answer 16

Freeze fracture reveals a plane through a specimen for examining structures like the cell membrane, while cryogenic electron microscopy provides a three-dimensional view of proteins involved in cellular function.

Question 17

What are advantages and limitations of electron microscopy compared to light microscopy?

Answer 17

EMs offer higher resolution but are expensive,
require extensive training,
and often involve non-living specimens, with artefacts sometimes present.
Light microscopy is used for living samples and employs techniques like fluorescent stains and immunofluorescence for enhanced visibility.

Question 18

How do fluorescent stains and immunofluorescence contribute to the study of living cells using light microscopy?

Answer 18

Fluorescent stains bind with cellular components, fluorescing when exposed to specific light, while immunofluorescence uses antibodies with dyes to detect target molecules, such as proteins, in living tissues or infected cells.

Question 19

What recent advancements have been made in fluorescence-based methods?

Answer 19

Modern fluorescence-based techniques allow visualization of single RNA molecules within single cells and viruses, expanding our ability to study RNA in detail.

Question 20

What is a characteristic of a brightfield microscope?

Answer 20

It uses visible light, the specimen is viewed against a light background, and it’s the most common and user-friendly light microscope.

Question 21

What distinguishes a darkfield microscope?

Answer 21

A darkfield microscope utilizes a special opaque lens in the condenser, blocking direct light from entering the specimen, resulting in the specimen appearing light against a dark background.

Question 22

What is a feature of a phase-contrast microscope?

Answer 22

It employs a special condenser with a circular diaphragm and a modified objective lens, allowing detailed imaging of specimens without staining.

Question 23

How are cells often categorized, and what are two major groups?

Answer 23

Cells are categorized into prokaryotic and eukaryotic cells. Prokaryotic cells are simpler and smaller than eukaryotic cells.

Question 24

What defines prokaryotic cells, and what organisms fall into this category?

Answer 24

Prokaryotic cells are typically less than 1 μm in diameter and include bacteria and archaea, which are mostly small, unicellular organisms.

Question 25

How do prokaryotic organisms relate to the evolution of life?

Answer 25

Bacteria and archaea, both prokaryotes, followed different evolutionary paths from eukaryotes (in the domain Eukarya). They play a significant role in the world today and exhibit vast diversity in factors like nutrition, energy sources, composition, and morphology.

Question 26

What are the features of a prokaryotic cell?

Answer 26

Cell wall Plasma membrane Flagella Pili Ribosomes Nucleoid (region containing free DNA)

Question 27

What are the functions of the prokaryotic cell wall?

Answer 27

The prokaryotic cell wall protects and maintains the cell's shape, preventing it from rupturing due to internal water pressure. It's primarily composed of peptidoglycan and, in some bacteria, contains an additional outer layer called the capsule, aiding in adhesion to surfaces.

Question 28

Describe the composition and function of the plasma membrane in prokaryotic cells.

Answer 28

The plasma membrane, similar to eukaryotic cells, is found just inside the cell wall. It controls material movement in and out of the cell and plays a role in prokaryotic cell division (binary fission).

Question 29

How is bacteria classification based on their dye retention?

Answer 29

Bacteria can be classified as "Gram-positive" or "Gram-negative" based on their reaction to crystal violet dye. Gram-positive bacteria retain the dye, appearing violet or blue, while Gram-negative bacteria do not retain the dye and do not appear violet or blue under a microscope.

Question 30

Can you provide examples of Gram-positive bacteria?

Answer 30

Bacillus and Staphylococcus are examples of Gram-positive bacteria.

Question 31

What are pili, and what functions do they serve in bacterial cells?

Answer 31

Pili are hair-like structures found on some bacterial cells, primarily used for attachment. Their main function involves joining bacterial cells in preparation for DNA transfer, facilitating a form of sexual reproduction.

Question 32

What purpose do flagella serve in bacterial cells?

Answer 32

Flagella, longer than pili, enable bacterial cells to move. They are anchored to the cell wall and plasma membrane, providing mobility to the cell.

Question 33

Describe the cytoplasm in prokaryotic cells.

Answer 33

The cytoplasm fills the entire interior of a prokaryotic cell. Under high-magnification microscopes, the most visible structure in the cytoplasm is the chromosome or DNA molecule. Prokaryotic cells lack internal membranes or specialized compartments within the cytoplasm where cellular processes occur.

Question 34

What role do ribosomes play in prokaryotic cells?

Answer 34

Ribosomes are the sites of protein synthesis in prokaryotic cells. Composed of protein and ribosomal RNA, they occur in large numbers in cells producing significant amounts of protein.

Question 35

Describe the nucleoid region in a bacterial cell.

Answer 35

The nucleoid region contains a single, continuous circular thread of DNA known as the bacterial chromosome. It lacks a surrounding membrane and is involved in cell control and reproduction. Prokaryotic DNA isn't associated with histones like in eukaryotes, hence bacterial chromosomes are often referred to as "naked loops".

Question 36

What are plasmids, and how do they differ from the bacterial chromosome?

Answer 36

Plasmids are small, circular DNA molecules independent of the main bacterial chromosome. They replicate separately and aren't necessary under normal conditions but aid the cell in adapting to unusual circumstances.

Question 37

Explain the process of binary fission in prokaryotic cell division

Answer 37

Prokaryotic cells divide through binary fission, where DNA is copied, resulting in two daughter chromosomes. These daughters attach to different regions on the plasma membrane, leading to the division of the cell into two genetically identical daughter cells.

Question 38

What distinguishes eukaryotic cells from prokaryotic cells?

Answer 38

Eukaryotic cells are found in organisms like algae, protozoa, fungi, plants, and animals, ranging in diameter from 5 to 100 μm. They contain a nucleus, noticeable at higher magnification, and various organelles that carry out specific functions, providing compartmentalization, unlike prokaryotic cells.

Question 39

What are organelles, and how do they contribute to eukaryotic cell functionality?

Answer 39

Organelles are cellular structures resembling organs in multicellular organisms, performing specialized functions. They enable compartmentalization in eukaryotic cells, segregating different chemical reactions and enhancing efficiency.

Question 40

Name some common organelles found in eukaryotic cells.

Answer 40

endoplasmic reticulum, ribosomes, lysosomes (not commonly in plant cells), Golgi apparatus, mitochondria, nucleus, chloroplasts (specific to plant and algal cells), centrosomes (in animals, but not most plant/fungal cells), and vacuoles.

Question 41

What is the cytoplasm in a eukaryotic cell, and what does it contain?

Answer 41

The cytoplasm in eukaryotic cells exists between the plasma membrane and nucleus, housing organelles. The fluid portion surrounding organelles is termed cytosol. It also includes a cytoskeleton, a network of fibres and rods, which prokaryotic cells lack.

Question 42

What are the functions and components of the cytoskeleton in eukaryotic cells?

Answer 42

The cytoskeleton maintains cell shape, anchors organelles, aids cellular movements, and facilitates organelle movement. It comprises actin filaments (microfilaments), intermediate filaments, and microtubules, adapting to internal and external environmental changes.

Question 43

Describe the structures and functions of the endoplasmic reticulum (ER) in eukaryotic cells.

Answer 43

The ER is an extensive network of tubules extending from the nucleus to the plasma membrane. It includes smooth ER, aiding lipid production, detoxification, and more; and rough ER, engaged in protein synthesis due to ribosomes on its surface.

Question 44

What role do ribosomes play in eukaryotic cells?

Answer 44

Ribosomes conduct protein synthesis within eukaryotic cells. They may be free in the cytoplasm or attached to the surface of the endoplasmic reticulum.

Question 45

Explain the functions of lysosomes in eukaryotic cells.

Answer 45

Lysosomes are intracellular digestive centers derived from the Golgi apparatus, containing hydrolytic enzymes to break down various molecules. They aid in recycling components and also break down materials from phagocytosis.

Question 46

What is the Golgi apparatus and its functions in eukaryotic cells?

Answer 46

The Golgi apparatus consists of flattened sacs called cisternae. It modifies, packages, and distributes materials synthesized in the cell, with vesicles transporting modified substances to their required destinations.

Question 47

Describe the structure and functions of mitochondria in eukaryotic cells.

Answer 47

Mitochondria are rod-shaped organelles with a double membrane and folded inner membrane (cristae). They produce ATP, often termed the powerhouse of the cell, and have their own DNA, ribosomes, and conduct cellular energy production.

Question 48

What is the significance of the cytoskeleton's structural diversity in eukaryotic cells?

Answer 48

The diversity of cytoskeletal elements—actin filaments, intermediate filaments, and microtubules—allows cells to adapt to various mechanical and functional demands, contributing to cell shape, movement, and structural integrity.

Question 49

How does the smooth ER's role in lipid production and detoxification impact cell function?

Answer 49

The smooth ER's ability to produce lipids and detoxify substances, particularly in liver cells, significantly contributes to membrane synthesis, hormone production, and drug detoxification processes within the cell.

Question 50

Differentiate between free ribosomes and those attached to the endoplasmic reticulum in terms of their protein synthesis function.

Answer 50

Free ribosomes synthesize proteins for use within the cytoplasm, while those attached to the ER synthesize proteins targeted for secretion, incorporation into membranes, or specific organelles.

Question 51

How do lysosomes contribute to maintaining cellular homeostasis and cell survival?

Answer 51

Lysosomes aid in cellular recycling by breaking down worn-out organelles and materials from outside the cell, facilitating nutrient retrieval and contributing to cellular renewal and overall cell health.

Question 52

Explain the significance of the Golgi apparatus in modifying and packaging cellular products.

Answer 52

The Golgi apparatus processes and modifies proteins and lipids synthesized by the ER, packaging them into vesicles for transport, secretion, or integration into cellular membranes.

Question 53

Explain how the arrangement of cristae and the presence of the matrix within mitochondria contribute to their role in ATP production.

Answer 53

The extensive folding of cristae increases the surface area available for cellular respiration, housing respiratory enzymes the matrix, a semi-fluid substance inside the inner membrane, contains mitochondrial DNA and ribosomes, both crucial for ATP synthesis and energy production within the cell.

Question 54

What is the structure of the nucleus in eukaryotic cells?

Answer 54

The nucleus in eukaryotic cells is enclosed by a double membrane known as the nuclear envelope, facilitating the segregation of DNA from the cell's cytoplasm. This envelope possesses pores enabling communication between the nucleus and cytoplasm.

Question 55

What is the role of DNA in the nucleus of eukaryotic cells?

Answer 55

DNA in the nucleus forms chromosomes, carrying vital genetic information necessary for the cell's existence and passing traits to subsequent generations. When not dividing, DNA exists as chromatin, comprising DNA strands and histone proteins, organized into nucleosomes, resembling a string of beads.

Question 56

What role do histones play in DNA organization within the cell nucleus?

Answer 56

Histones are proteins crucial for DNA packaging and regulation within the nucleus. They possess a positive charge that interacts with the DNA's negative charge, forming complexes around which DNA wraps, aiding in organizing and regulating DNA accessibility for cellular processes.

Question 57

What is chromatin, and what are its primary forms?

Answer 57

Chromatin refers to the complex of DNA and proteins in the eukaryotic nucleus. It exists as euchromatin, less condensed and conducive to gene expression, and heterochromatin, highly condensed and typically transcriptionally inactive, regulating gene expression, DNA replication, and repair.

Question 58

What constitutes a nucleosome, and what is its function in DNA packaging?

Answer 58

A nucleosome consists of DNA strands wrapped around a histone octamer, comprising two each of histones H2A, H2B, H3, and H4. This arrangement forms a bead-like structure, providing structural organization for DNA while allowing dynamic access for essential cellular processes like DNA replication, transcription, and repair.

Question 59

How does the absence or presence of a nucleus impact cellular functions and reproduction?

Answer 59

Cells lacking a nucleus lose the ability to reproduce but often exhibit increased specialization for specific functions. For instance, human red blood cells, which lack nuclei, specialize in gas transportation.

Question 60

What essential role do nucleoli play within the nucleus of eukaryotic cells?

Answer 60

Nucleoli are dark areas within nuclei responsible for manufacturing ribosome molecules. Ribosomal components are produced within nucleoli and then pass through the nuclear envelope to assemble as functional ribosomes.

Question 61

In which types of cells are chloroplasts typically found, and what features do they share with prokaryotic cells?

Answer 61

Chloroplasts are present in plant and algae cells. They share similarities with prokaryotic cells such as possessing their own DNA, 70S ribosomes, and a double membrane structure resembling the size of a bacterial cell.

Question 62

Describe the internal structure of a chloroplast and its components involved in photosynthesis.

Answer 62

Internally, a chloroplast consists of grana, thylakoids, and stroma. Grana are stacks of thylakoids, flattened sacs containing structures necessary for light absorption—a crucial initial step in photosynthesis. The stroma, akin to cytoplasm, contains enzymes and compounds vital for completing the photosynthetic process.

Question 63

What fundamental process do chloroplasts undertake, and what is the outcome of this process?

Answer 63

Chloroplasts conduct photosynthesis, converting light energy into chemical energy. This chemical energy, captured from sunlight, is utilized to synthesize sugars from carbon dioxide, which serve as energy-rich molecules in the cell.

Question 64

What is the function of centrioles in the centrosome, and how are they positioned in animal cells?

Answer 64

Centrioles within the centrosome facilitate microtubule assembly, providing structural support and enabling cellular movement and division. In animal cells, these centrioles are typically oriented at right angles to each other.

Question 65

Do plant and fungal cells possess centrioles, and how do they contribute to microtubule formation?

Answer 65

Plant and fungal cells lack centrioles, yet they generate microtubules from centrosome-like regions, suggesting that centrioles are not indispensable for microtubule production.

Question 66

What is the significance of basal bodies in relation to cilia and flagella, and where are they typically located?

Answer 66

Basal bodies, associated with the centrosome, are situated at the base of cilia and flagella in eukaryotic cells. They are believed to direct the assembly of microtubules within these structures, though not all cells possess cilia or flagella.

Question 67

Describe the role and diverse functions of vacuoles in cells, particularly in plants and animals.

Answer 67

Vacuoles, membrane-bound storage organelles often originating from the Golgi apparatus, perform various roles. They store nutrients, metabolic waste, toxins, and water. In plant cells, vacuoles help maintain rigidity by absorbing water and contribute to the overall surface area-to-volume ratio in cells.

Question 68

three differences between prokaryotic and eukaryotic cells.

Answer 68

Prokaryotic cells have DNA in a ring form without proteins, contain DNA free in the cytoplasm (nucleoid region), lack mitochondria, possess 70S ribosomes, and lack internal compartmentalization for organelle formation. Eukaryotic cells, on the other hand, exhibit DNA as chromosomes/chromatin with proteins, enclose DNA within a nuclear envelope (nucleus), contain mitochondria, have 80S ribosomes, and feature internal compartmentalization forming various organelles.

Question 69

What are the key similarities shared by prokaryotic and eukaryotic cells?

Answer 69

Both types of cells possess an outer boundary involving a plasma membrane, conduct all the functions of life, and contain DNA within their structures.

Question 70

What are some unique functions performed by unicellular organisms to maintain life processes?

Answer 70

Unicellular organisms utilize the cell membrane to control material movement and maintain homeostasis, store waste in vacuoles to prevent harm, use cilia or flagella for environmental response and movement, conduct digestion within vacuoles for nutrition, generate energy through mitochondria or enzyme areas, and utilize ribosomes for growth and repair.

Question 71

How do multicellular organisms manage life functions compared to unicellular organisms?

Answer 71

Multicellular organisms often delegate life functions to entire groups of cells forming organs. Rather than individual cells performing functions, specialized groups of cells within organs execute tasks such as digestion, waste management, movement, energy production, and growth or repair.

Question 72

What composes the exterior structure of fungal cells, and what's located just inside this outer layer?

Answer 72

Fungal cells feature an outer cell wall composed of chitin and house a plasma membrane just inside this protective outer layer.

Question 73

How do fungal cells differ from plant cells concerning carbohydrate production?

Answer 73

Unlike plant cells, fungal cells lack chloroplasts for carbohydrate production but store carbohydrates as glycogen in their numerous, small vacuoles.

Question 74

Do fungal cells possess cilia or flagella, and do they have associated basal bodies?

Answer 74

Fungal cells may have cilia or flagella but lack associated basal bodies unlike other cell types.

Question 75

What functions does the cell wall serve in fungal cells, and what's unique about their centrosomes?

Answer 75

The cell wall provides both flexibility and support to fungal cells, allowing variation in cell shape. Fungal cells possess centrosomes but lack centrioles.

Question 76

What unique feature is seen in some fungi's hyphae, and what's the outcome of this structure?

Answer 76

Some fungi produce hyphae without cross-walls, resulting in a single mass of cytoplasm containing multiple nuclei.

Question 77

Describe the specialized features of phloem sieve tube elements in multicellular plants.

Answer 77

Phloem sieve tube elements possess end walls with pores and minimal cellular components. They form tube structures and rely on companion cells to remain functional.

Question 78

What distinguishes human red blood cells in terms of structure and function?

Answer 78

Red blood cells are specialized for oxygen transport, containing high amounts of haemoglobin. They lack a nucleus, allowing more space for oxygen and facilitating their role in oxygen transport.

Question 79

Name two specialized cell types and their unique structures related to their functions.

Answer 79

Nerve cells are elongated with branched connections to transmit electrical impulses, while sperm cells have a tail for movement, many mitochondria, and an enzyme-producing head to penetrate egg cells.

Question 80

What purpose do the cells associated with the lungs serve, and what unique feature aids in their function?

Answer 80

These cells possess tiny hairs called cilia on their exterior, working collectively to move mucus and particles out of the airways.

Question 81

What are the key points of the endosymbiotic theory regarding the origin of eukaryotic cells?

Answer 81

About 2 billion years ago, a larger cell with a nucleus engulfed a smaller prokaryotic cell capable of energy production. These cells developed a mutually beneficial relationship, resulting in the smaller cell evolving into mitochondria.

Question 82

How do the characteristics of mitochondria support the endosymbiotic theory?

Answer 82

Mitochondria share similarities with prokaryotic cells: they're of similar size, divide independently, have their own DNA and ribosomes, produce proteins, and have a double membrane structure consistent with engulfment.

Question 83

What evidence do chloroplasts in plant cells provide for the theory of endosymbiosis?

Answer 83

Hatena arenicola and Elysia chlorotica demonstrate symbiotic relationships with green algae, switching their nutritional modes and incorporating chloroplasts. This adaptation supports the idea of symbiosis leading to chloroplast incorporation.

Question 84

How does the relationship between Elysia chlorotica and green algae support the theory of endosymbiosis?

Answer 84

Elysia chlorotica, in its adult stage, retains functional chloroplasts from ingested green algae, allowing it to conduct photosynthesis. This process parallels the endosymbiotic theory, highlighting the acquisition and retention of chloroplasts to sustain a more sedentary lifestyle reliant on light.

Question 85

How does the similarity in DNA code between mitochondria and bacteria support the endosymbiotic theory?

Answer 85

Mitochondrial DNA closely resembles bacterial DNA, indicating a common ancestry. The universality of the genetic code across organisms supports their relatedness from a common origin.

Question 86

What marked the appearance of prokaryotes according to the timeline constructed for life on Earth?

Answer 86

Prokaryotes appeared approximately 3.5 billion years ago.

Question 87

When did single-celled eukaryotes emerge based on the life timeline on Earth?

Answer 87

Single-celled eukaryotes appeared around 1.8 billion years ago.

Question 88

At what point did multicellular eukaryotes arise according to the constructed Earth's life timeline?

Answer 88

Multicellular eukaryotes emerged roughly 1.2 billion years ago.

Question 89

What significant event occurred 2.2 billion years ago according to the timeline of life on Earth?

Answer 89

Atmospheric oxygen appeared around 2.2 billion years ago.

Question 90

When did ocean animals come into existence based on the constructed Earth's life timeline?

Answer 90

Ocean animals emerged approximately 535 million years ago.

Question 91

Around what time did land animals first appear according to the timeline of life on Earth?

Answer 91

Land animals appeared roughly 500 million years ago.

Question 92

What is a key process that facilitated the development of the cell and led to specialization within it?

Answer 92

Compartmentalization through the formation of membranes played a significant role, allowing efficient reactions and processes within the cell.

Question 93

How did the appearance of multicelled eukaryotes affect the specialization of cells within organisms?

Answer 93

Multicelled eukaryotes led to the differentiation of cells within organisms into highly specialized tissues and organs.

Question 94

How do mechanisms within multicellular organisms control and coordinate gene expression?

Answer 94

Specialized mechanisms regulate gene expression, enabling differentiation and responding to diverse environments within multicellular organisms.

Question 95

How has multicellularity impacted life on Earth?

Answer 95

Multicellularity, through the coordination and communication among cells, tissues, and organs, has enabled life forms to thrive in a wide range of environments on Earth.