Chapter 2: Cells, Viruses and Reproduction of Living Things Flashcards
2.1 Eukaryotic and prokaryotic cell structure and function
Describe the cell theory
Cell theory is a unifying concept that states that cells are the fundamental unit of structure, function, and organization in all living organisms.
2.1 Eukaryotic and prokaryotic cell structure and function
How can magnification and resolution be achieved in microscopy?
Magnification and resolution can be achieved using light and electron microscopy techniques.
2.1 Eukaryotic and prokaryotic cell structure and function
Discuss the importance of staining specimens in microscopy.
Staining specimens in microscopy is important as it enhances contrast, allowing for better visualization of cellular structures.
2.1 Eukaryotic and prokaryotic cell structure and function
Explain the organization of cells in complex organisms.
In complex organisms, cells are organized into tissues, organs, and organ systems.
2.1 Eukaryotic and prokaryotic cell structure and function
Identify the key components of prokaryotic cells.
Prokaryotic cells have ultrastructural components such as nucleoid, plasmids, 70S ribosomes, and a cell wall.
2.1 Eukaryotic and prokaryotic cell structure and function
What are the features of bacterial cell walls?
- Prevent water entry by osmosis, maintaining cell shape.
- Made of peptidoglycan, a polymer of sugar and peptide chains.
- Some have a capsule/slime layer for nutrient storage and immune protection.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the function of pili and flagella in bacteria?
- Pili (fimbriae): Aid attachment and reproduction in bacteria like E. coli.
- Flagella: Enable movement via rapid rotation (100 revolutions per second), made of flagellin protein.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the function of the bacterial cell surface membrane?
- Controls the exchange of substances like in eukaryotic cells.
- Can replace mitochondria for respiration in some bacteria.
- Contains mesosomes, possibly aiding in DNA separation and respiration.
2.1 Eukaryotic and prokaryotic cell structure and function
What are plasmids and their function in bacteria?
- Small, circular DNA molecules separate from the main bacterial chromosome.
- Often contain genes for antibiotic resistance or toxin production.
- Can be transferred between bacteria via pili.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the nucleoid in bacterial cells?
- Contains bacterial DNA, usually a single, circular molecule.
- Not enclosed in a membrane.
- Occupies a significant area of the cell.
2.1 Eukaryotic and prokaryotic cell structure and function
What are 70S ribosomes in bacteria and their function?
Smaller than eukaryotic 80S ribosomes.
Responsible for protein synthesis.
Consist of two subunits and function similarly to eukaryotic ribosomes.
2.1 Eukaryotic and prokaryotic cell structure and function
What is Gram staining, and how does it differentiate bacterial cell walls?
Differentiates bacteria based on cell wall composition.
Gram-positive bacteria: Thick peptidoglycan layer with teichoic acid, retains crystal violet stain (blue/purple).
Gram-negative bacteria: Thin peptidoglycan layer, outer membrane with lipopolysaccharides, stains red with safranin.
2.1 Eukaryotic and prokaryotic cell structure and function
What are examples of the gram positive and gram negative bacteria?
Gram-Positive: Staphylococcus aureus, Streptococcus pneumoniae.
Gram-Negative: Escherichia coli, Salmonella spp.
2.1 Eukaryotic and prokaryotic cell structure and function
What do all typical animal cells contain?
Contains structures common to all eukaryotic cells, including plants and fungi.
Cell surface membrane:
Cytoplasm.
Nucleus
- all together forming the protoplasm.
Cytoplasm: Houses essential components for cell functions and survival.
2.1 Eukaryotic and prokaryotic cell structure and function
Describe the membrane of a eukaryotic cell
- Act as an outer boundary to the cell.
- Internal (intracellular) membranes compartmentalize the cell.
- Functions:
- Control movement of substances.
- House enzymes for reactions (e.g., respiration, photosynthesis).
- Form compartments (e.g., lysosomes for hydrolytic enzymes).
2.1 Eukaryotic and prokaryotic cell structure and function
Describe what the protoplasm is
Initially thought to be structureless but contains many organelles.
Revealed by the electron microscope to be full of sub-cellular structures.
2.1 Eukaryotic and prokaryotic cell structure and function
Describe the nucleus of eukaryotic cells
- Largest organelle, size: 1–20 µm.
- Visible under light microscopy; electron microscopy reveals:
- Spherical shape surrounded by double nuclear membrane.
- Nuclear membrane contains pores for material exchange.
Contains: - Nucleic acids (DNA and RNA) and proteins.
- DNA binds to proteins to form chromatin when not dividing.
- Nucleolus, which produces ribosomes and plays a role in cell growth/division.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the function, structure, and theory of the mitochondria?
- They are the site of cellular respiration, producing ATP to meet energy demands.
- A double membrane with the inner membrane folded into cristae to increase surface area, and a matrix where reactions occur.
- It allows mitochondria to replicate independently within the cell.
- They evolved from bacteria that were incorporated into early eukaryotic cells.
2.1 Eukaryotic and prokaryotic cell structure and function
Describe centrioles in terms of structure, location and function.
- Near the nucleus, usually in pairs.
- Centrioles are bundles of nine microtubules, measuring about 0.5 µm long and 0.2 µm wide.
- They are involved in cell division by forming a spindle of microtubules to move chromosomes.
2.1 Eukaryotic and prokaryotic cell structure and function
Describe the cytoskeleton in terms of structure, components, functions
- It is a dynamic, 3D web-like structure filling the cytoplasm in eukaryotic cells.
- Microfilaments (protein fibers) and microtubules (tiny tubes about 20 nm in diameter).
- It provides structure to the cytoplasm, keeps organelles in place, and assists with cell movement and transport.
2.1 Eukaryotic and prokaryotic cell structure and function
What proteins are microtubules related to in muscle cells?
Actin and Myosin
2.1 Eukaryotic and prokaryotic cell structure and function
Can prokaryotic cells have a cytoskeleton?
Some prokaryotic cells also have a cytoskeleton
2.1 Eukaryotic and prokaryotic cell structure and function
Describe vaculoes in terms of the structure, function and if animal cells have them.
- They form and dissolve as needed.
- They act as food vacuoles or help control water content (contractile vacuoles).
- Permanent vacuoles are never seen in higher animal cell
2.1 Eukaryotic and prokaryotic cell structure and function
What are the differences between 80S and 70S ribosomes?
- 80S ribosomes: Found in eukaryotic cells; made of a 40S small subunit and 60S large subunit (1:1 RNA:protein ratio).
- 70S ribosomes: Found in mitochondria, chloroplasts, and prokaryotes; made of a 30S small subunit and 50S large subunit (2:1 RNA:protein ratio).
- 70S ribosomes are evidence of endosymbiosis, showing mitochondria and chloroplasts evolved from bacteria.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the function of the Golgi apparatus?
- Stacked, flattened membranes (cisternae) modify, sort, and package proteins and lipids.
- Proteins from RER are processed and sent to their destinations via vesicles.
- Adds carbohydrates to proteins (forming glycoproteins) and produces lysosomes.
- Orientation: Cis face receives proteins; Trans face releases finished products.
2.1 Eukaryotic and prokaryotic cell structure and function
What are the structues and differences between the rER and sER?
- Rough ER (RER): Studded with ribosomes; synthesizes proteins for secretion and membranes.
- Smooth ER (SER): No ribosomes; synthesizes lipids and steroids, detoxifies chemicals, and stores calcium.
- Structure: RER has ribosomes attached, SER is tubular.
- Cells involved in secretion (e.g., digestive enzymes) have more RER, while those in lipid metabolism (e.g., liver) have more SER.
2.1 Eukaryotic and prokaryotic cell structure and function
If a cell needs to be destroyed which organelle is used?
Lysosomes. It can release its enzymes to rupture the cells and can self destruct.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the plant cell wall made of, and what are its key characteristics?
- Composed of cellulose microfibrils held together by hydrogen bonds.
- Freely permeable to water and solutes unless impregnated with suberin or lignin (e.g., in cork or wood).
2.1 Eukaryotic and prokaryotic cell structure and function
What is the middle lamella, and what is its function?
- First layer formed during cell division.
- Made of pectin, which acts as a glue to bind neighboring cells together.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the primary cell wall, and what are its properties?
- Flexible and composed of cellulose microfibrils.
- Microfibrils are oriented in the same direction to allow the wall to stretch as the cell grows.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the secondary cell wall, and how does it differ from the primary cell wall?
- Forms as the cell matures and becomes more rigid.
- Contains additional cellulose layers and lignin, providing extra strength and rigidity.
- Found in structures like plant fibers, making them durable for uses like rope and paper.
2.1 Eukaryotic and prokaryotic cell structure and function
What are plasmodesmata, and why are they important?
- Cytoplasmic bridges between plant cells, enabling communication and substance exchange.
- Lined by the cell membrane and allow cytoplasm to pass through, forming the symplast (shared cytoplasmic system).
- Essential for coordinated cell activity, growth, and tissue development (e.g., plant grafts).
2.1 Eukaryotic and prokaryotic cell structure and function
What is the permanent vacuole, and what surrounds it?
The permanent vacuole is a large, fluid-filled space in plant cells, surrounded by a membrane called the tonoplast.
2.1 Eukaryotic and prokaryotic cell structure and function
What are the main functions of the permanent vacuole?
- Maintains cell shape and turgor pressure by filling with cell sap.
- Stores pigments, waste products, chemicals, and proteins.
- Plays a role similar to lysosomes in animal cells, containing enzymes for digestion.
- Regulates water potential and stores secondary metabolites.
- Ensures rigidity through osmosis, keeping the cytoplasm pressed against the cell wall.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the structure of the chloroplast?
Surrounded by a double membrane with an inner membrane forming thylakoids (stacked into grana).
Contains stroma, chlorophyll, ribosomes, starch grains, and DNA for semi-autonomous function.
2.1 Eukaryotic and prokaryotic cell structure and function
What is the function of the chloroplast?
Chloroplasts are the site of photosynthesis, converting light energy into glucose and oxygen.
Chlorophyll captures light energy for the light-dependent and light-independent reactions.
2.1 Eukaryotic and prokaryotic cell structure and function
What are amyloplasts, where are they found, and function?
- Amyloplasts are colorless plastids derived from leucoplasts, specialized for starch storage.
- Found in high-starch areas like potato tubers and storage tissues.
- Store starch as an energy reserve.
- Convert starch into glucose when energy is needed.
2.2 Viruses
What type of virus is each of the following:
human immunodeficiency virus,λ (lambda) phage,tobacco mosaic virus,Ebola
λ (lambda) phage-DNA
tobacco mosaic virus and Ebola-RNA
human immunodeficiency virus-RNA retrovirus
2.2 Viruses
What are viruses, and why are they not considered living organisms?
Viruses are obligate intracellular parasites that can only survive and reproduce inside host cells. They are not considered living because they lack cellular structure and cannot perform metabolic processes independently.
2.2 Viruses
What are the basic components of a virus?
Viruses have a capsid (protein coat made of capsomeres) that protects their genetic material, which can be DNA or RNA. Some viruses also have a lipid envelope derived from the host cell.
2.2 Viruses
What makes enveloped viruses more vulnerable?
The lipid envelope, derived from the host cell membrane, makes enveloped viruses more susceptible to detergents and disinfectants.
2.2 Viruses
What are RNA viruses, and how do they differ?
RNA viruses contain RNA as their genetic material.
Positive-sense RNA viruses: Can be directly translated into proteins.
Negative-sense RNA viruses: Require transcription into positive-sense RNA before translation.
2.2 Viruses
What are retroviruses, and how do they replicate?
Retroviruses are RNA viruses, like HIV, that use reverse transcriptase to synthesize DNA from RNA, which is then integrated into the host genome.
2.2 Viruses
How do viruses reproduce?(general)
Viruses infect by attaching to host cells using virus attachment particles (VAPs) on their surface.
Host specificity depends on compatibility with host cell receptors.
Virus injects genetic material into the host cell, hijacking its machinery for replication.
Plant viruses often use vectors (e.g., aphids) to penetrate cell walls.
2.2 Viruses
What is latency in the lysogenic pathway of DNA viruses?
- The viral DNA integrates into the host’s genome as a provirus and replicates with the host DNA during cell division.
- A repressor protein prevents the expression of viral genes, stopping the production of viral components.
- The virus does not harm the host cell or cause illness during this phase.
- This latent phase, called lysogeny, allows the virus to remain dormant as part of the host’s reproducing cells.
2.2 Viruses
What is the lytic cycle in a virus?
The lytic cycle is a viral replication process where the virus infects a host cell, uses the host’s machinery to produce new viral particles, and eventually causes the host cell to burst (lyse), releasing new viruses.
2.2 Viruses
What are the key steps of the lytic cycle?
The key steps of the lytic cycle are:
Attachment: The virus binds to the host cell surface.
Entry: The viral genetic material enters the host cell.
Replication: The virus uses the host’s machinery to replicate its genetic material and produce viral proteins.
Assembly: New viral particles are assembled inside the host cell.
Lysis: The host cell bursts, releasing the new viruses to infect other cells.
2.2 Viruses
How does the lytic cycle affect the host organism?
The lytic cycle damages the host cell by causing it to burst, which can lead to tissue damage and symptoms of illness in the host organism.
2.2 Viruses
Describe the lysogenic cycle. Identify all periods including what cycle it may shift into.
Attachment and Entry:
* The virus attaches to the host cell and injects its genetic material (DNA or RNA) into the host.
* Integration:
* The viral genetic material is incorporated into the host cell’s DNA. Once integrated, the viral DNA is called a provirus.
Dormancy (Lysogeny):
* The provirus remains dormant within the host’s DNA. During this time:
* The viral genes are not expressed.
* The host cell’s normal functions continue unaffected.
* The provirus is copied along with the host DNA during cell division.
Reactivation:
* Under certain conditions (e.g., stress, UV radiation, or chemical triggers), the dormant provirus is activated and enters the lytic cycle.
Switch to Lytic Cycle:
* The viral genetic material is expressed, producing new viruses.
* The host cell eventually lyses, releasing new viral particles.
2.2 Viruses
Draw the lysogenic and lytic cycle
2.2 Viruses
What are positive ssRNA viruses?
Viruses with a single sense strand of RNA that is used directly as mRNA for protein translation, producing viral structural proteins and RNA polymerase to replicate viral RNA.
2.2 Viruses
What are negative ssRNA viruses?
Viruses with a single antisense strand of RNA, transcribed into a sense strand by RNA replicase to act as mRNA for protein translation, producing RNA replicase for viral RNA replication and new virus formation.
2.2 Viruses
How do antivirals work?
Antivirals work by inhibiting virus replication within the host cells.
2.2 Viruses
What is an RNA retrovirus, and how does it replicate?
Retroviruses, like HIV, use RNA as their genetic material.
RNA is converted into DNA by reverse transcriptase after entering the host cell.
The DNA integrates into the host genome as a provirus.
The provirus directs the synthesis of new viral RNA, mRNA, and proteins.
New viral particles are assembled and released, continuing the infection cycle.
2.2 Viruses
Draw the process of the RNA retrovirus lifecycle
2.2 Viruses
What are vaccinations and how do they work?
Vaccinations introduce a weakened or inactive form of a virus into the body. This triggers the immune system to produce antibodies against the virus, providing immunity if you are later exposed to the actual virus.
2.2 Viruses
What can be learned from the 2014 Ebola outbreak about disease control?
The outbreak showed that early prevention and containment efforts are essential to manage and stop the spread of highly contagious viruses.
2.2 Viruses
What are some key measures for controlling the spread of viral diseases?
Handwashing and hygiene
Isolation of infected individuals
Sterilizing equipment and bedding
Identifying and monitoring contacts of infected individuals
Vaccination (when available)
2.2 Viruses
What are some challenges in controlling viral diseases in developing countries?
Limited access to healthcare infrastructure (e.g., isolation units)
Lack of resources for rapid disease identification and testing
Cultural practices that may facilitate disease transmission (e.g., funeral rituals)
2.2 Viruses
How do antiviral drugs work?
Antiviral drugs target specific stages of the viral replication cycle, such as:
Binding to viral receptors
Inhibiting viral enzymes
Preventing the release of new virus particles
2.2 Viruses
What are some key features of the Ebola virus and its transmission?
Severe viral illness with high mortality rates.
Transmitted through contact with infected bodily fluids (blood, feces, secretions).
Can spread from person to person through direct contact or contaminated surfaces.
2.2 Viruses
What is an epidemic?
An epidemic occurs when the number of cases of a disease in a population is significantly higher than expected over a given period.
2.2 Viruses
What are some ethical considerations in using untested drugs during epidemics?
Balancing the potential benefits of the drug with the risks to human safety.
Ensuring informed consent from patients participating in clinical trials.
Prioritizing access to experimental treatments for those most in need
2.3 Eukaryotic cell cycle and division
What are the main stages of the cell cycle?
Interphase, mitosis, and cytokinesis.
2.3 Eukaryotic cell cycle and division
What happens to genetic material during the cell cycle?
It contributes to growth, repair, and asexual reproduction.
2.3 Eukaryotic cell cycle and division
What does meiosis result in?
Haploid gametes, including the stages of meiosis.
2.3 Eukaryotic cell cycle and division
What processes allow meiosis to contribute to genetic variation?
Through recombination of alleles, including independent assortment and crossing over.
2.3 Eukaryotic cell cycle and division
What is the function of chromosomes in cell division?
Chromosomes carry genetic information and ensure that DNA is accurately replicated and distributed to daughter cells during cell division. They condense during division for easier identification.
2.3 Eukaryotic cell cycle and division
How is DNA packaged efficiently within the cell?
DNA is wrapped around positively charged proteins called histones, forming nucleosomes, which further coil to create denser chromatin structures.
2.3 Eukaryotic cell cycle and division
What is the appearance of chromosomes in non-dividing cells?
In non-dividing cells, chromosomes are translucent and difficult to distinguish individually.
2.3 Eukaryotic cell division
What is the number of chromosomes in each cell and how is this maintianed before division?
Human cells contain 46 chromosomes (23 pairs from each parent).
Before mitosis, DNA is duplicated to ensure each new cell gets a complete set of genetic information
2.3 Eukaryotic cell division
How can chromosomes be arranged to show strucutre?
Chromosomes can be stained and arranged in a karyotype to analyze their structure and number.
Karyotypes show the 22 pairs of autosomes and one pair of sex chromosomes (XX or XY).
2.3 Eukaryotic cell division
What is the function of the cell cycle?
Cells divide to support growth, repair, and reproduction.
The process follows a sequence known as the cell cycle.
2.3 Eukaryotic cell division
Describe interphase
A period of non-division.
The cell grows, increases its mass and size.
DNA replication occurs.
2.3 Eukaryotic cell division
What occurs in mitosis (general)
The active division phase where the cell splits into two identical daughter nuclei.
2.3 Eukaryotic cell division
What occurs in cytokinesis (general)
The final stage where the cytoplasm divides, separating the two new cells.
2.3 Eukaryotic cell cycle and division
What happens to chromosomes before division?
When the cell prepares to divide, chromosomes condense and become denser.
2.3 Eukaryotic cell cycle and division
Describe the G1 phase of the cell cycle?
The interval between the previous mitotic division and DNA replication.
The cell grows, increases its materials, and prepares for DNA synthesis.
Cells can stay in G₁ for hours, days, or even months depending on the tissue type.
2.3 Eukaryotic cell cycle and division
Describe the S phase of cell cycle
DNA replication occurs.
Chromosomes duplicate into sister chromatids in preparation for cell division.
2.3 Eukaryotic cell cycle and division
Describe G2 Phase
Organelles and proteins necessary for cell division are synthesized.
The cell ensures it is ready for division.
2.3 Eukaryotic cell cycle and division
Describe the M phase
The cell actively divides its genetic material.
2.3 Eukaryotic cell cycle and division
Describe the C phase
The final separation of the two daughter cells.
2.3 Eukaryotic cell cycle and division
What is mitosis?
The process where a cell divides to produce two genetically identical daughter cells.
2.3 Eukaryotic cell cycle and division
What is asexual reproduction?
The process where a cell divides to produce two genetically identical daughter cells.
2.3 Eukaryotic cell cycle and division
What is sexual reproduction?
Offspring are genetically different due to the combination of genes from two parents.
2.3 Eukaryotic cell cycle and division
What is meiosis?
A type of cell division reducing chromosome number by half to form gametes.
2.3 Eukaryotic cell cycle and division
What are histones?
Positively charged proteins that aid in DNA coiling.
2.3 Eukaryotic cell cycle and division
What are karyotypes?
A visual representation of chromosomes in a cell.
2.3 Eukaryotic cell cycle and division
What are CDKs?
Enzymes that regulate the cell cycle through protein phosphorylation.
2.3 Eukaryotic cell cycle and division
What is interphase?
The phase where the cell increases in size and replicates DNA.
2.3 Eukaryotic cell cycle and division
What is a chromatid?
A single strand of a duplicated chromosome.
2.3 Eukaryotic cell cycle and division
Describe prophase
The genetic material (DNA) has already been replicated, producing identical copies of chromosomes.
Each chromosome consists of two identical sister chromatids, held together at a region called the centromere.
Chromosomes condense, coil up, and become visible under a microscope.
The nucleolus breaks down and disappears.
Centrioles start moving to opposite poles of the cell.
They appear as star-like structures called asters, as microtubules begin forming.
The spindle fibers start forming, pulling apart chromosomes.
2.3 Eukaryotic cell cycle and division
Describe metaphase
The nuclear membrane breaks down completely.
Centrioles position themselves at opposite poles of the cell.
Spindle fibers, composed of microtubules, extend across the cell, forming the spindle apparatus.
Chromosomes align along the center of the cell, known as the metaphase plate or equator.
Each chromosome’s centromere is attached to a spindle fiber, ensuring proper alignment.
Chromosomes appear to jostle for position before settling at the metaphase plate.
2.3 Eukaryotic cell cycle and division
Describe anaphase
The centromeres split, allowing the sister chromatids to separate completely.
The separated chromatids are now considered individual daughter chromosomes.
The spindle fibers pull the daughter chromosomes to opposite poles of the cell.
This movement occurs rapidly, within minutes.
Chromosomes rely on microtubules of the spindle for movement, as they cannot move independently.
The overlapping microtubules contain contractile fibers similar to those in muscle cells.
These fibers contract, pulling chromatids apart using energy from cellular respiration.
By the end of anaphase, two complete sets of chromosomes have reached the opposite poles.
2.3 Eukaryotic cell cycle and division
Describe telophase
The spindle fibers begin to break down and disassemble.
A nuclear envelope reforms around each set of chromosomes at opposite poles.
Chromosomes begin to uncoil, becoming less distinct under the microscope.
The nucleolus reappears, signaling the end of nuclear division.
Centrioles are re-formed, preparing the cell for future divisions.
2.3 Eukaryotic cell cycle and division
Describe cytokinesis
The final stage of the cell cycle, involving the division of the cytoplasm.
In animal cells, cytokinesis occurs through:
A ring of contractile fibers tightens around the center of the cell, forming a cleavage furrow, which pinches the cell into two daughter cells.
In plant cells, cytokinesis occurs differently:
Golgi vesicles align at the cell’s equator, fusing to form a cell plate.
The cell plate gradually extends outward, forming new cell walls that separate the daughter cells.
Small gaps called plasmodesmata remain between cells to allow communication.
The two newly formed daughter cells prepare for their own cycle of growth and division.
2.3 Eukaryotic cell cycle and division
Draw a cell in interphase
2.3 Eukaryotic cell cycle and division
Draw a cell in prophase
2.3 Eukaryotic cell cycle and division
Draw a cell in metaphase
2.3 Eukaryotic cell cycle and division
Draw a cell in anaphase
2.3 Eukaryotic cell cycle and division
Draw a cell in telophase
2.3 Eukaryotic cell cycle and division
Draw a plant cell in cytokinesis
2.3 Eukaryotic cell cycle and division
What are strategies for asexual reproduction dependent on, and what are examples?
- Strategies depend on mitosis.
- Examples include:
- Producing spores.
- Regeneration.
2.3 Eukaryotic cell cycle and division
When does meiosis occur?
ONLY to produce sex gametes
2.3 Eukaryotic cell cycle and division
What is sporulation, and where is it commonly observed?
- Involves mitosis to produce asexual spores.
- Spores grow into new individuals, survive harsh conditions, and spread over long distances.
- Common in fungi and plants like mosses and ferns.
2.3 Eukaryotic cell cycle and division
What is regeneration, and how does fragmentation fit into this process?
Regeneration:
Replacement of lost body parts, such as lizards regrowing tails.
Fragmentation:
Organisms reproduce from body fragments (e.g., starfish).
Observed in fungi, flatworms, algae, and sponges.
Basis for artificial cloning in plants.
2.3 Eukaryotic cell cycle and division
What is budding in a reproductive sense, and where is it commonly found?
Budding:
Involves an outgrowth from the parent organism.
Produces a smaller, identical individual via mitotic cell division.
The bud eventually detaches and lives independently.
Common in yeast cells and organisms like Hydra.
Hydra can reproduce both asexually (budding) and sexually.
2.3 Eukaryotic cell cycle and division
What is vegetative propagation, and how does it occur?
Vegetative propagation:
A specialized form of budding in plants.
Develops into a fully differentiated new plant identical to the parent.
Propagation can occur from the stem, leaf, or root.
Stored carbohydrates allow propagation under adverse conditions.
Methods include natural processes (e.g., runners) and artificial techniques (e.g., cuttings).
2.3 Eukaryotic cell cycle and division
How does parthenogenesis occur in Komodo dragons, and why is it significant?
Answer:
Parthenogenesis is reproduction without fertilization, seen in 80 species of vertebrates.
Komodo dragons can reproduce via WW or WZ chromosomes (females WW = infertile; WZ = male offspring).
Occurs in isolated environments without males.
Challenges traditional views of reptile reproduction.
2.3 Eukaryotic cell cycle and division
What are gametes and how do they contribute to sexual reproduction?
Question: What are gametes and how do they contribute to sexual reproduction?
Answer:
Gametes: Specialized sex cells involved in reproduction.
Diploid (2n) cells: Contain two sets of chromosomes (pairs).
Haploid (n) cells: Contain a single set of chromosomes to maintain species’ chromosome number during fertilization.
Fertilization fuses two haploid cells to form a diploid zygote, preventing an exponential chromosome increase.
Male gametes: Spermatozoa (sperm) from testes.
Female gametes: Ova (eggs) from ovaries.
2.3 Eukaryotic cell cycle and division
What is meiosis and why is it important?
Meiosis: A cell division that halves chromosome numbers in gametes.
Occurs only in sex organs (testes and ovaries in animals; anthers and ovules in flowering plants).
Ensures genetic diversity and stability in chromosome numbers across generations.
Difference from mitosis:
Mitosis produces identical diploid cells; meiosis produces genetically diverse haploid cells.
Meiosis involves two rounds of division, resulting in four unique daughter cells.
Produces microspores (male) and megaspores (female) in flowering plants.
Allows species to evolve via genetic variation.
2.3 Eukaryotic cell cycle and division
How do chromosomes behave during meiosis?
Meiosis involves two divisions:
First division (Meiosis I): Homologous chromosomes pair up and separate.
Second division (Meiosis II): Sister chromatids separate.
Key processes:
Crossing over (recombination): Homologous chromosomes exchange DNA at chiasmata, increasing genetic variation.
Independent assortment: Random orientation of homologous pairs results in different genetic combinations.
Final result:
Four haploid cells, each genetically unique.
Ensuring genetic variation
2.3 Eukaryotic cell cycle and division
Where are gametes formed, and how does this differ in plants and animals?
In animals:
Male gonads = testes, producing sperm.
Female gonads = ovaries, producing ova.
In plants:
Male organs = anthers, producing pollen (male gametes).
Female organs = ovules, producing egg cells.
Gametes are temporary in simpler plants but stored in complex organisms.
Formation involves specialized meiotic division to ensure the correct chromosome number in offspring.
2.3 Eukaryotic cell cycle and division
What is independent assortment, and why is it important in meiosis?
Independent assortment refers to the random distribution of maternal and paternal chromosomes into gametes during meiosis.
Each gamete receives 23 chromosomes, with any number (from 0 to 23) coming from either parent.
2.3 Eukaryotic cell cycle and division
What is crossing over, and why is it important in meiosis?
Crossing over occurs when large multi-enzyme complexes cut and join parts of maternal and paternal chromatids.
The points where chromatids break are called chiasmata.
Significance:
It introduces genetic variation by exchanging genetic material.
Errors during crossing over can lead to mutations, further diversifying the genetic makeup of a species.
2.3 Eukaryotic cell cycle and division
Draw a diagram outlining the possible effects of crossing over
Diagram should follow same rules as picture below:
2.4 Sexual reproduction in mammals
What are the characteristics of sperm?
Small (50-60 μm), motile, and numerous.
Specialized to deliver genetic material to the ovum.
Includes:
Head: Contains the nucleus and acrosome (enzymes for penetrating the ovum).
Middle piece: Packed with mitochondria for energy.
Tail: Whip-like motion propels the sperm.
2.4 Sexual reproduction in mammals
What are the characteristics of ova?
Large (100 μm), few in number, and nutrient-rich.
Contain food reserves for the developing embryo.
Surrounded by a zona pellucida (jelly-like protective layer).
2.4 Sexual reproduction in mammals
Draw a labelled diagram of a sperm and ova
2.4 Sexual reproduction in mammals
What are the structures protecting the ovum and their roles?
The ovum at ovulation is a secondary oocyte with one polar body.
It is surrounded by a jelly-like layer called the zona pellucida and some follicle cells.
Many sperm cluster around the ovum.
The acrosome reaction is triggered when sperm touch the surface of the ovum, releasing enzymes to:
Digest follicle cells.
Digest the zona pellucida.
2.4 Sexual reproduction in mammals
What role do enzymes play during fertilisation?
Enzymes are released from the sperm’s acrosome.
These enzymes digest the follicle cells and zona pellucida, helping sperm penetrate the protective layers of the ovum.
A single sperm alone cannot produce sufficient enzymes to penetrate the ovum.
The large number of sperm in ejaculation ensures enough sperm are present to digest the defences.
2.4 Sexual reproduction in mammals
How does a sperm successfully penetrate and fertilise the ovum?
One sperm wiggles through weakened protective barriers and touches the oocyte’s surface membrane.
The oocyte completes its second meiotic division, forming a haploid egg nucleus.
The sperm’s haploid nucleus fuses with the egg’s haploid nucleus to form a diploid zygote
2.4 Sexual reproduction in mammals
What mechanisms prevent polyspermy during fertilisation?
Polyspermy would result in a nucleus containing too many sets of chromosomes.
To prevent this:
Ion channels in the ovum’s cell membrane close, and the inside of the cell becomes positively charged.
A tough fertilisation membrane forms around the fertilised ovum, repelling further sperm.
The electrical charge returns to normal after the membrane forms.
2.4 Sexual reproduction in mammals
What happens in the final stages of fertilisation?
The head of the sperm enters the oocyte, while its tail remains outside.
Inside the ovum:
The sperm releases its chromosomes, which fuse with the ovum’s chromosomes.
A diploid zygote is formed.
Fertilisation is now complete, and a new individual begins to develop.
This process is also called conception.
2.5 Sexual reproduction in plants
What are the 2 life cycle phases of plant gametogenesis?
- sporophyte generation
- gametophyte generation
2.5 Sexual reproduction in plants
What occurs in gametophyte generation?
Haploid gametes are formed via mitosis.
The diploid spores become gametophytes via mitosis and then the gametes become a zygote by 2 fusing together.
2.5 Sexual reproduction in plants
What occurs in sporophyte generation?
Diploid spores are formed via meiosis.
The zygote undergoes mitosis becoming a sporphyte and then via meiosis becoming diploid spores.
2.5 Sexual reproduction in plants
The phases of gametogenesis are combined in…
flowering plants
2.5 Sexual reproduction in plants
In terms of the products of gametogenesis:
The main plant boyd is ….(1)
Parts of the anther and ovary are…(2)
- Diploid sporophytes
- Haploid gametophytes
2.5 Sexual reproduction in plants
Draw the process of alternation of generation
2.5 Sexual reproduction in plants
Draw a labelled diagram of a plant
2.5 Sexual reproduction in plants
What makes up the stamen?
Anther and filament
2.5 Sexual reproduction in plants
What makes up the carpel?
stigma, style and ovary
2.5 Sexual reproduction in plants
How is pollen formed?
Meiosis occurs at the anther creating many pollen grain which contain male gametes
2.5 Sexual reproduction in plants
How many pollen sacs does each anther contain?
4-Each have many microspore mother cells (diploid)
2.5 Sexual reproduction in plants
Diploid microspores (mother cells) divide by…
meiosis creative haploid microspores, which are the gametophyte generation. The gametes themselves are formed from the gametophyte generation.
2.5 Sexual reproduction in plants
Gametes are formed from microspores via…
mitosis.
2.5 Sexual reproduction in plants
What does each microspore contain?
Two nuclei. One is the generative nuclei which fuses with the ovule nuclei. The other is the tube nuclei which produces the pollen tube.
2.5 Sexual reproduction in plants
What produces ovules in an ovary?
Meosis produces ovules in ovaries
2.5 Sexual reproduction in plants
How is an ovule attached to the ovary?
Via placenta which is then covered in a nucellus in a centre of this emryo sac where the gametophyte generation forms.
2.5 Sexual reproduction in plants
How does the diploid megaspore form?
It divides to form 4 haploid megaspores. Three of these are degenerate and form the antipodal cells, while one undergoes 3 mitotic divisions leaving an embryo sac containing an egg cell, two polar nuclei, 3 antipodal cells and 2 synergids
2.5 Sexual reproduction in plants
What is a synergid?
direct pollen tube growth downwards (toward female gametophyte) and facilitate entrance of tube to embryo sac.
2.5 Sexual reproduction in plants
What is an antipodal cell?
provide nutrients to support developing embryo
2.5 Sexual reproduction in plants
What is pollination?
- Pollination is the process of transferring pollen from the anthers of one plant to the stigma of another (of the same species).
- After this, a pollen tube grows down the stigma carrying the male gamete to the ovary where it fuses with an ova (fertilisation).
- This will then develop into a fruit.
2.5 Sexual reproduction in plants
Draw a diagram describing the formation of an egg cell in plants
2.5 Sexual reproduction in plants
What is a pollinator?
Pollinators can be insects (particularly bees), or other animals that can move pollen around (or have the pollen stick to them as they move around).
2.5 Sexual reproduction in plants
What is external fertilisation?
- Takes place outside the plant
- Relies on chance
- Male and femail gametes fuse in the environment (usually aquatic)
2.5 Sexual reproduction in plants
What is the process of plant fertilisation until germination?
- Male gamete is contained in pollen grain, while the female gamete is deep in the ovarian tissue.
- Pollen lands on the surgace of the stigma of the flower during pollination
- Molecules on the surface of stigma and pollen grain interact.
- If same species, grain grows (germinates)
2.5 Sexual reproduction in plants
What is internal fertilisation?
- Higher chance of fertilisation than external
- Involves males releasing sperm into the females body, in some instances males can deposit a package of sperm for the females to pick up
- More common in land animals
2.5 Sexual reproduction in plants
What is the process of plant fertilisation after germination?
- Pollen tube grows out of tube cell through the stigma and style
- Tip produces hydrolytic enzymes digesting the style tissue so pollen tube makes it way down the cell
- Digested tissue acts as a nutrient source for the tube as it grows
- Generative nucleus travels down pollen tube in the generative cell
- Nucleus divides to form 2 male nuclei
- Eventually tip of pollen tube passes through micropule of ovule
- 2 male nuclei pass through micropyle
- Double fertilisation occurs
- One male nuclei fuses with two polar nuclei to form endosperm
- Endosperm is involved in supplying the embryo plant food
- Other male nucleus fuses with egg cell to form zygote
- Seed and embryo development begins
2.5 Sexual reproduction in plants
Draw the process of fertilisation as a labelled diagram
