IB Biology Chp 1 questions
Eukaryotic cells have intracellular and extracellular components. State the functions of one named extracellular component.
(plant cell wall) strengthens/supports the cell/plant (against gravity); prevents the entry of pathogens; maintains the shape of plant cells; allows turgor pressure/high pressure to develop inside the cell; prevents excessive entry of water to the cell;
Outline the endosymbiotic theory.
- Mitochondria and chloroplasts share similar characteristics so it is believed that prokaryotes were engulfed by eukaryotes during endocytosis (instead of being digested they became an organelle of a eukaryote). - Characteristics: smaller 70S ribosomes; makes proteins; transcribe DNA and use mRNA for circular DNA; similar size and shape; binary fission; double membrane. - Valuable: ability to produce organic molecules and make ATP.
Discuss the advantages and disadvantages of the use of adult stem cells.
Advantages: a. «adult stem cells» can divide «endlessly» / can differentiate b. «adult stem cells» can be used to repair/regenerate «tissues» c. fewer ethical objections «than with embryonic stem cells» d. adults can give «informed» consent for use of their stem cells e. adult source is not killed / «source» would not have grown into new human / no death of embryos used to provide stem cells f. no rejection problems / patient's own cells used g. less chance of cancer/«malignant» tumor development «than from embryonic stem cells» h. most tissues in adults contain some stem cells Disadvantages: i. difficult to obtain/collect/find in adult body/very few available j. some «adult» tissues contain few/no stem cells k. «adult stem cells» differentiate into fewer cell types «than embryonic cells
Outline two properties of RNA that would have allowed it to play a role in the origin of life
>RNAs can store, transmit and replicate genetic Information >Ribozymes are RNA molecules that can catalyse reactions >Some can polymerise nucleotides using ATP Some can break chemical bonds, including peptide bonds >Ribosomes are themselves Ribozymes. The part that catalyses the peptide bonds is RNA, the protein part of a ribosome seems to have a purely structural function > Evolution by natural selection requires variation and heritability. RNA possesses these traits
18) What feature of cell membranes allows endocytosis to occur? A. Fluidity of phospholipid bilayer B. Presence of protein pumps C. Presence of carrier proteins D. Glycoprotein binding sites
A
4) What provides evidence for the endosymbiotic theory? A. Mitochondrial DNA in eukaryotic cells B. 70S ribosomes in prokaryotic cells C. Gene transfer from prokaryotic cells to eukaryotic cells using plasmids D. Prokaryotic cells (Escherichia coli) in the large intestine digest proteins
A
Animal cells often secrete glycoproteins as extracellular components. What is a role of these glycoproteins? A. Adhesion B. Additional energy reserve C. Membrane fluidity D. Water uptake
A
During which stage does the cell surface area to volume ratio decrease? A. Interphase B. Metaphase C. Telophase D. Cytokinesis
A
How can cells in a multicellular organism differentiate? A. They express some of their genes but not others. B. They all have a different genetic composition. C. Different cells contain a different set of chromosomes. D. Different cells do not have some of the genes.
A
What evidence from the image of Paramecium indicates whether the organism is a prokaryote or a eukaryote? A. Compartments in the cell indicate that it is a eukaryote. B. No nucleus indicates that the cell is a prokaryote. C. Lack of a cell wall indicates that the cell is a eukaryote. D. It is a unicellular organism, so it must be a prokaryote.
A
What is an example of binary fission? A. Cell division in prokaryotes B. Production of haploid gametes C. Separation of chromatids in prokaryotic cells D. Replication of prokaryotic DNA occurring simultaneously in two directions
A
Which characteristic of stem cells makes them useful for treating Stargardt's disease? A. They can differentiate into retinal cells. B. They are readily available from especially created embryos. C. They transport white blood cells to the eyes. D. They divide by binary fission so provide sufficient cells.
A
Which functions of life are found in all unicellular organisms? A. growth, response and nutrition B. differentiation, response and nutrition C. metabolism, meiosis and homeostasis D. growth, metabolism and differentiation
A
Which of these processes require mitosis? A. Embryological development B. Reducing surface area to volume ratio C. Maintaining cell size D. Cell growth
A
Discuss the endosymbiotic theory for the origin of eukaryotes.
An endosymbiont is a cell which lives inside another cell with mutual benefit Eukaryotic cells are believed to have evolved from aerobic prokaryotes that were engulfed by endocytosis Mitochondria and chloroplasts are suggested to have originated by endosymbiosis Evidence supporting the theory of endosymbiosis: Mitochondria and chloroplasts have their own DNA (which is naked and circular) Mitochondria and chloroplasts have ribosomes that are similar to prokaryotes (70S) Mitochondria and chloroplasts have a double membrane and the inner membrane has proteins similar to prokaryotes Mitochondria and chloroplasts are roughly the same size as bacteria and are susceptible to the antibiotic chloramphenicol
Outline natural methods of cloning in some eukaryotes.
Animal Cloning Methods Binary Fission The parent organism divides equally in two, so as to produce two genetically identical daughter organisms This method of cloning occurs in Planaria (flatworms) but is also common to bacteria and protists (e.g. euglena, amoeba) Budding Cells split off the parent organism, generating a smaller daughter organism which eventually separates from the parent This method of cloning occurs in Hydra but is also common to many species of yeast Fragmentation New organisms grow from a separated fragment of the parent organism This method of cloning is common to starfish and certain species of annelid worms Plant Cloning Methods Plants have the capacity for vegetative propagation, whereby small pieces can be induced to grow independently This is because adult plants possess meristematic tissue capable of cellular differentiation (totipotent) Virtually all types of roots and shoots are capable of vegetative propagation Garlic and onion bulbs are modified plant leaves - all the bulbs in a group are genetically identical Underground stems (e.g. potato tubers) can form new plants which are genetically identical to the parent plant Certain plants can form horizontal stems called runners (or stolons) that grow roots and develop into clones Some plants (mainly algae, mosses and ferns) can reproduce asexually by producing spores Spores are also produced by certain types of bacteria and fungi
2) What is a function of the plant cell wall? A. Formation of vesicles for transport of large molecules B. Prevention of excessive water uptake C. Communication with other cells by means of glycoproteins D. Active transport of ions
B
During which phase of the cell cycle do chromosomes duplicate? A. G1 B. S C. G2 D. Mitosis
B
In a cell, what is the effect of a large surface area to volume ratio? A. Slower rate of exchange of waste materials B. Faster heat loss C. Faster rate of mitosis D. Slower intake of food
B
What can the extracellular matrix of cells be made of? I. Polysaccharide II. Glycoprotein III. Phospholipid A. I only B. I and II only C. II and III only D. I, II and III
B
What do prokaryotic cells have that eukaryotic cells do not? A. Mitochondria B. 70S ribosomes C. Histones D. Internal membranes
B
What happens during the G2 stage of interphase? A. Homologous chromosomes pair B. Synthesis of proteins C. Homologous chromosomes separate D. Replication of DNA
B
What is a difference between a cell in the G1 phase and a cell in the G2 phase of the cell cycle? A. A cell in the G2 phase would be smaller than a cell in the G1 phase. B. A cell in the G2 phase would have more mitochondria than a cell in the G1 phase. C. A cell in the G1 phase would have more DNA in its chromosomes than a cell in the G2 phase. D. DNA replication occurs in the G1 phase but not in the G2 phase
B
What is a role of cholesterol in animal cells? A. It increases body fat. B. It controls membrane fluidity. C. It lines the inner wall of capillaries. D. It is a constituent of bile.
B
What is produced as a result of mitosis? A. Two cells, each containing half the number of chromosomes of the original cell B. Two cells, each containing the same number of chromosomes as the original cell C. Four cells, each containing the same number of chromosomes as the original cell D. Four cells, each containing half the number of chromosomes of the original cell (
B
What route is used to export proteins from the cell? A. Golgi apparatus → rough endoplasmic reticulum → plasma membrane B. Rough endoplasmic reticulum → Golgi apparatus → plasma membrane C. Golgi apparatus → lysosome → rough endoplasmic reticulum D. Rough endoplasmic reticulum → lysosome → Golgi apparatus
B
Which evidence falsifies the Davson-Danielli model? I. The presence of globular proteins within the phospholipid bilayer II. Non-polar amino acids cause proteins to remain embedded in membranes III. Membrane proteins remain in a fixed position inside a membrane A. I only B. I and II only C. II and III only D. I, II and III
B
Which feature of striated muscle cells allows them to be considered as a possible exception to the cell theory? A. They are found in multicellular organisms. B. They contain more than one nucleus. C. They are specialized for movement. D. They do not carry out mitosis.
B
Which of the following structures does Escherichia coli have? I. 70S Ribosomes II. Pili III. Nucleus A. I only B. I and II only C. II and III only D. I, II and III
B
18) What are stem cells? A. Specialized cells that can be used therapeutically B. Surplus cells taken from an embryo C. Cells that retain their ability to divide and differentiate D. Cells in the xylem and phloem tissues that support a plant
C
An unknown cell is observed using a microscope. A cell wall, ribosomes and DNA are identified. What can be concluded from these observations? A. It can only be a prokaryotic cell. B. It can only be a eukaryotic cell. C. It could be a prokaryotic or eukaryotic cell. D. It can only be a plant cell.
C
The DNA of a particular cell is damaged, so that the cell continues to divide uncontrollably. What is the possible result? A. Coronary heart disease B. AIDS C. Tumour formation D. Down syndrome
C
What do diffusion and osmosis have in common? A. They only happen in living cells. B. They require transport proteins in the membrane. C. They are passive transport mechanisms. D. Net movement of substances is against the concentration gradient
C
What does therapeutic cloning involve? A. Developing genetically identical cultures of human cells for use in drug testing B. Helping infertile couples to conceive by injecting the father's sperm into the mother's egg C. Producing embryonic stem cells for medical use D. Replacing a mutant allele in an embryo to prevent genetic disease
C
What feature do plant cells have but not animal cells? A. Plasma membranes B. Mitochondria C. Cell walls D. 80S ribosomes
C
What is the approximate thickness of the plasma membrane of a cell? A. 10 nm B. 50 nm C. 10 µm D. 50 µm
C
What is the correct order of increasing size for the following biological structures? I. The width of a virus II. The width of a bacterium III. The thickness of a cell surface membrane IV. The diameter of a eukaryotic cell A. I III II IV B. I III IV II C. III I II IV D. III II I IV
C
What is the function of the Golgi apparatus? A. Transport of lipids B. Synthesis of polypeptides C. Processing of proteins for secretion D. Generation of most of the cell's supply of ATP
C
When observing the behaviour of a vesicle in a cell, what identifies it as a vesicle only involved in exocytosis? A. Adhesion between two lipid bilayers B. Fusion of two membranes C. Secretion of material D. Invagination of a plasma membrane
C
Which are functions of membrane proteins? A. Hormone binding sites and DNA replication B. Cell adhesion and translation C. Cell to cell communication and protein pumps D. Passive transport and glycosis
C
Which functions of life are carried out by all unicellular organisms? A. Response, homeostasis, growth and photosynthesis B. Metabolism, ventilation, reproduction and nutrition C. Response, homeostasis, metabolism and growth D. Reproduction, ventilation, response and nutrition
C
Which of the following characteristics found in a structure necessarily indicates that it is alive? A. The presence of genetic material B. The presence of a lipid bilayer C. Metabolism D. Movement
C
Which of the following does not occur during interphase? A. Replication B. Translation C. Cytokinesis D. An increase in the number of mitochondria
C
Which of the following is not a function performed by a membrane protein? A. Hormone binding sites B. Cell adhesion C. Enzyme synthesis D. Pumps for active transport
C
Which of the following will contribute to the cell theory? I. Living organisms are composed of cells. II. All cells come from pre-existing cells by mitosis. III. Cells are the smallest units of life. A. I only B. II only C. I and III only D. I, II and III
C
Explain the importance of surface area to volume ratio as a limit to cell size.
Cells need to produce chemical energy (via metabolism) to survive and this requires the exchange of materials with the environment As a cell grows, volume (units3) increases faster than surface area (units2), leading to a decreased SA:Vol ratio If metabolic rate exceeds the rate of exchange of vital materials and wastes (low SA:Vol ratio), the cell will eventually die Hence growing cells tend to divide and remain small in order to maintain a high SA:Vol ratio suitable for survival
4) The giant alga Acetabularia has a feature that suggests it is an exception to the cell theory. What feature is this? A. It lacks a nucleus. B. It lacks a cell wall. C. It has only one mitochondrion. D. It lacks subdivision into separate cells.
D
A cell has cytoplasm, a cell wall, naked DNA and ribosomes. Based on this information, what type of cell could this be? A. A cell from a pine tree B. A grasshopper cell C. A human red blood cell D. A bacterium
D
Cells in the adrenal gland produce the hormone epinephrine and store it in vesicles. To release epinephrine these vesicles are carried to the plasma membrane and fuse with it. What process is occurring? A. Expulsion B. Exchange C. Excretion D. Exocytosis
D
During reproduction in flowering plants an embryo sac is produced, containing one haploid nucleus. This haploid nucleus divides by mitosis three times. What is produced? A. One diploid nucleus B. Four diploid nuclei C. Four haploid nuclei D. Eight haploid nuclei
D
How do prokaryotic cells divide? A. By mitosis B. By meiosis C. By budding D. By binary fission
D
In viewing an electron micrograph of a cell, ribosomes, pili and a single circular chromosome are observed. What other structure is likely to be present? A. The rough endoplasmic reticulum (rER) B. Mitochondria C. A nuclear membrane D. A plasmid
D
In which of the following cells can more than one nucleus be found? A. An unfertilized egg B. Neuron C. Sertoli cell D. Muscle fibre
D
What structures are part of an Escherichia coli cell? A. Ribosomes, nucleoid and Golgi apparatus B. Ribosomes, mitochondria and pili C. Cell wall, plasma membrane and nuclear membrane D. Pili, flagella and cytoplasm
D
Where are proteins synthesized by free ribosomes used? A. Outside the cell after secretion B. Within the nucleus C. Within the lysosomes D. Within the cytoplasm
D
Which of the following is a feature of exocytosis but not endocytosis? A. Shape changes of a membrane B. Vesicle formation C. Use of ATP D. Secretion
D
Which of the following structures are found in all cells? A. Mitochondria B. Cell walls C. Chloroplasts D. Ribosomes
D
Which of the following structures are present in both plant and animal cells? I. Cell wall II. Chloroplast III. Mitochondrion A. I only B. I and II only C. I and III only D. III only
D
Which statement is part of the cell theory? A. Cells are composed of organic molecules. B. Cells have DNA as their genetic material. C. Cells have cytoplasm surrounded by a membrane. D. Cells come from pre-existing cells
D
Why do multicellular organisms have emergent properties? A. They have more genes than unicellular organisms. B. Properties of unicellular organisms are enhanced by having many cells. C. All of their genes are expressed whereas unicellular organisms express only some. D. They show properties that can only result from the interaction of many cells.
D
b. Which structure is found in E. coli, but not in a eukaryotic cell? A. Cell wall B. Endoplasmic reticulum C. Cytoplasm D. Pili
D
Explain how the base sequence of DNA is conserved during replication
DNA replication is semi-conservative; DNA is split into two single/template strands; nucleotides are assembled on/attached to each single/template strand; by complementary base pairing; adenine with thymine and cytosine with guanine / A with T and C with G; strand newly formed on each template strand is identical to other template strand; DNA polymerase used;
The difference between mitosis in plants and animals
Finally, cytokinesis is the last stage during which the cytoplasm divides to create two daughter cells. In animal cells the cell is pinched in two while plant cells form a plate between the dividing cells.
Explain how chemical bonding between water molecules makes water a valuable coolant in living organisms.
Hydrogen bonding between molecules makes it a valuable coolant in living organisms. Breaking hydrogen bonds needs energy, and removes heat.
Outline how molecules move across a membrane by simple diffusion.
In simple diffusion, small noncharged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration (they move down their concentration gradient).
State three processes occurring in a cell during interphase of the cell cycle but not in mitosis.
Interphase is an active period in the life of a cell - many events need to occur before a cell can successfully undergo division: Protein synthesis: The cell needs to synthesise key proteins and enzymes to enable it to grow, copy its contents and then divide ATP production: The cell will need to generate sufficient quantities of ATP in order to successfully divide Increase number of organelles: The cell needs to ensure both daughter cells will have the necessary numbers of organelles needed to survive DNA replication: The genetic material must be faithfully duplicated before division (this occurs during the S phase)
Outline how transport occurs across membranes by facilitated diffusion.
Larger, polar substances (ions, macromolecules) cannot freely diffuse and require the assistance of transport proteins (carrier proteins and channel proteins) to facilitate their movement (facilitated diffusion)
State the functions of the following organelles of a eukaryotic animal cell: lysosome, Golgi apparatus, free ribosomes, plasma membrane, rough endoplasmic reticulum.
Lysosome: Breakdown / hydrolysis of macromolecules Golgi Apparatus: Involved in the sorting, storing, modification and export of secretory products Free ribosomes: Site of polypeptide synthesis (this process is called translation) plasma membrane: Semi-permeable and selective barrier surrounding the cell rough ER: Transports proteins between organelles
Outline the experiments of Miller and Urey into the origin of organic compounds
Miller and Urey recreated the conditions of pre-biotic Earth in a closed system consisting of a series of flasks and tubes These conditions included a reducing atmosphere (low oxygen), high radiation levels, high temperatures and electrical storms Water was boiled to form vapour and then was mixed with methane, ammonia and hydrogen The mixture of gases was exposed to an electrical discharge (sparks) to simulate lightning The mixture was then allowed to cool and after one week was found to contain some simple amino acids and complex oily hydrocarbons Based on these findings, it was concluded that under the hypothesised conditions of pre-biotic Earth, organic molecules could be formed
Explain how mitosis produces two genetically identical nuclei.
Mitosis is divided into four stages; prophase, metaphase, anaphase and telophase. During prophase, the chromosomes become visible under a light microscope as they super coil and therefore they get shorter and more bulky. The nuclear envelope disintegrates and the spindle microtubules grow and extend from each pole to the equator. At metaphase the chromatids move to the equator. The sister chromatids are two DNA molecules formed by DNA replication and are therefore identical. These sister chromatids are then separated in anaphase as the spindle microtubules attaches to centromere and pulls the sister chromatids to opposite poles. As the sister chromatids separate they are called chromosomes. This means that each pole has the same chromosomes (same genetic material). Finally the microtubules break down, the chromosomes uncoil and the nuclear membrane reforms. The cell then divides into two daughter cells with genetically identical nuclei
Discuss possible locations where conditions would have allowed for the synthesis of organic compounds
Organic synthesis requires the presence of a range of inorganic molecules and an energy source to combine them into organic forms Locations where such conditions may have existed in the past include: Hydrothermal vents: Regions of the ocean floor where superheated water is released from the Earth's crust Volcanoes: Intensive volcanic activity could provide sufficient thermal activity either on land or under the seabed Extraterrestrial locations: Other planets (e.g. Mars) may have been subjected to appropriate conditions (compound transfer via meteorites)
Define osmolarity
Osmolarity is a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)
Describe the movement of water across membranes
Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration until equilibrium is reached. Passes through protein channels/ selectively-permeable membrane;
Describe how the functions of life are performed in Paramecium and Chlamydomonas:
Paramecium: Nutrition Feeds on smaller organisms by ingesting them and digesting them in food vesicles Growth Increases in size and dry mass by accumulating organic matter and absorbing minerals from its food Metabolism Produce enzymes that catalyze many chemical reactions in the cytoplasm Response Reacts to stimuli: Reverses its direction of movement when it touches a solid object Excretion Expels waste products of metabolism: CO2 from cell respiration diffuses out of the cell Reproduction Produce asexually using mitosis and sexually using meiosis and gametes Homeostasis Keep internal condition within limits, i.e expels excess water using contractile vacuoles Nutrition Produces its own food by photosynthesis using chloroplast which occupies most of the cell Growth Increases in size and dry mass due to photosynthesis and absorption of minerals Metabolism Produce enzymes that catalyze many chemical reactions in the cytoplasm Response Reacts to stimuli: Senses where the brightest light is with its eye spot and swim towards it Excretion Expels waste products of metabolism: O2 from photosynthesis diffuses out of the cell Reproduction Produce sexually using mitosis and asexually using meiosis and gametes Homeostasis Keep internal condition within limits, i.e expels excess water using contractile vacuoles
Distinguish between active and passive movements of materials across plasma membranes, using named examples.
Passive: Diffusion:The net movement of particles from a region of high concentration to a region of low concentration (along the gradient) until equilibrium No energy needed down concentration gradient no pumps needed Eg: oxygen across alveoli Active transport: Pinocytosis requires energy/ATP against concentration gradient; requires protein pumps; glucose absorption in ileum /
Explain how the properties of phospholipids help to maintain the structure of cell membranes.
Phospholipid molecules make up the cell membrane and are hydrophilic (attracted to water) as well as hydrophobic (not attracted to water but are attracted to other hydrophobic tails). The membrane is principally held together by the relatively weak hydrophobic associations between phospholipids. They have a hydrophilic phosphate head and two hydrophobic hydrocarbon tails. Cell membranes are made up of a double layer of these phospholipid molecules. This is because in water the hydrophilic heads will face the water while the hydrophobic tails will be in the center because they face away from the water. The phospholipid bilayer makes the membrane very stable but also allows flexibility. The phospholipid in the membrane are in a fluid state which allows the cell to change it's shape easily.
State two differences in structure between plant and animal cells.
Plants have cell wall and chloroplast which animals cells dont
Outline how vesicles are used to transport materials secreted by a cell
Polypeptides destined for secretion contain an initial target sequence (a signal recognition peptide) which directs the ribosome to the endoplasmic reticulum The polypeptide continues to be synthesised by the ribosome into the lumen of the ER, where the signal sequence is removed from the nascent chain The polypeptide within the rough ER is transferred to the golgi apparatus via a vesicle, which forms from the budding of the membrane The polypeptide moves via vesicles from the cis face of the golgi to the trans face and may be modified along the way (e.g. glycosylated, truncated, etc.) The polypeptide is finally transferred via a vesicle to the plasma membrane, whereby it is either immediately released (constitutive secretion) or stored for a delayed release in response to some cellular signal (regulatory secretion = for a more concentrated and more sustained effect) Eg: hormone secretion
Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere.
Remember: there was little free oxygen in the early atmosphere. Small amounts were made by UV light splitting water vapour in the atmosphere >After about 2 billion years of prokaryote life (2 billion years ago) there was an Earth changing event: a form of chlorophyll appeared in bacteria that allowed oxygenic photosynthesis >The increase in Oxygen led to: 1) The breakdown of the chemicals in the 'chemical soup' to carbon dioxide and oxidized sediments. 2) The formation of the ozone layer, which blocked out UV and stopped the production of more of the 'soupy' molecules > The oxygen concentration rose to 0.45% of the atmosphere. Not much compared to today's 21%, but it coincides with the rise of the Eukaryotes
Outline the effects of putting plant tissue in a hypertonic and hypotonic solution.
Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration ⇒ gains water) Solutions with a relatively lower osmolarity are categorised as hypotonic (low solute concentration ⇒ loses water) Solutions that have the same osmolarity are categorised as isotonic (same solute concentration ⇒ no net water flow) The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
Outline one therapeutic use of stem cells.
Stargardt's disease is a genetic disease that causes photoreceptive cells to degenerate and the vision to become progressively worse. Researchers have developed methods which can enable embryonic stem cells to divide into retina cells. The retina cells are then injected In the eyes . When the injected cells attach to the retina and divide, it improves the vision of the patient.
Outline the use of human embryonic stem cells (hESC) to treat Stargardt's disease.
Stargardt's disease is a genetic disease that causes photoreceptive cells to degenerate and the vision to become progressively worse. Researchers have developed methods which can enable embryonic stem cells to divide into retina cells. The retina cells are then injected In the eyes . When the injected cells attach to the retina and divide, it improves the vision of the patient.
Describe the characteristics of stem cells that make them potentially useful in medicine.
Stem cells are cells that retain their ability to divide and differentiate into various cell types
Outline the cell theory
The cell theory states that: 1. All living things are composed of cells (or cell products) 2. The cell is the smallest unit of life 3. Cells only arise from pre-existing cells
Outline the stages of the cell cycle.
The first stage of cell division is interphase which is divided into 3 phases; G1, S and G2. The cell cycle starts with G1 (Gap phase 1) during which the cell grows larger. This is followed by phase S (synthesis) during which the genome is replicated. Finally, G2 (gap phase 2) is the second growth phase which separates the newly replicated genome and marks the end of interphase. The fourth stage is mitosis which is divided into prophase, metaphase, anaphase and telophase. During mitosis the spindle fibers attach to the chromosomes and pull sister chromatids apart. This stage separates the two daughter genomes. Finally, cytokinesis is the last stage during which the cytoplasm divides to create two daughter cells. In animal cells the cell is pinched in two while plant cells form a plate between the dividing cells.
Define osmosis.
The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration until equilibrium is reached
Compare simple diffusion with facilitated diffusion as mechanisms to transport solutes across membranes.
The plasma membrane is semi-permeable and selective in what can cross Substances that move along the concentration gradient (high to low) undergo passive transport and do not require the expenditure of energy (ATP) Simple diffusion: Small, non-polar (lipophilic) molecules can freely diffuse across the membrane Facilitated diffusion: Larger, polar substances (ions, macromolecules) cannot freely diffuse and require the assistance of transport proteins (carrier proteins and channel proteins) to facilitate their movement (facilitated diffusion)
Describe the process of endocytosis.
The process by which large substances (or bulk amounts of smaller substances) enter the cell without travelling across the plasma membrane An invagination of the membrane forms a flask-like depression which envelopes the material; the invagination is then sealed off forming a vesicle There are two main types of endocytosis: 1. Phagocytosis The process by which solid substances (e.g. food particles, foreign pathogens) are ingested (usually to be transported to the lysosome for break down) 2. Pinocytosis The process by which liquids / solutions (e.g. dissolved substances) are ingested by the cell (allows quick entry for large amounts of substance)
Describe the process off exocytosis
The process by which large substances exit the cell without travelling across the plasma membrane Vesicles (usually derived from the golgi) fuse with the plasma membrane expelling their contents into the extracellular environment
Outline four different functions of membrane proteins.
Transport: Protein channels (facilitated) and protein pumps (active) Receptors: Peptide-based hormones (insulin, glucagon, etc.) Anchorage: Cytoskeleton attachments and extracellular matrix Cell recognition: MHC proteins and antigens Intercellular joinings: Tight junctions and plasmodesmata Enzymatic activity: Metabolic pathways (e.g. electron transport chain)
What is the sequence of stages during the cell cycle? A. G1 → S → G2 → mitosis → cytokinesis B. mitosis → G1 → G2 → cytokinesis → S C. G1 → G2 → S → mitosis → cytokinesis D. G1 → G2 → mitosis → cytokinesis → S
a
2) What occurs during meiosis but not mitosis? A. Spindles are formed from microtubules. B. Chromosome number is conserved. C. Homologous chromosomes pair up. D. Centromeres split.
c
5) Which events occur during both mitosis and meiosis? A. Production of haploid cells from diploid cells B. Crossing over C. Separation of the chromatids from each chromosome D. Production of genetically different cells
c
Escherichia coli is a unicellular organism, so each cell must carry out all of the processes required for life. Outline the functions of each of the structures in the cells of Escherichia coli.
cell wall protects the cell from damage; cell wall prevents the cell from bursting; plasma membrane pumps substances/carries out active transport; plasma membrane controls entry and exit of substances; cytoplasm contains enzymes that carry out metabolism; pili are used to connect bacterial cells/can pull bacteria closer together; flagella used for locomotion/movement of the bacterial cell; ribosomes synthesize proteins; (naked) DNA of main chromosome is located in the nucleoid (region); nucleoid initiates reproduction/binary fission; (naked) DNA/chromosome/nucleoid controls/determines cell structure/function; plasmids confer (luxury) functions such as disease resistance/ antibiotic resistance/other; capsule protects cell/promotes adherence;
4) What is evidence for the endosymbiotic theory? A. RNA can catalyse metabolic reactions. B. Meteorites contain organic molecules. C. Amino acids can be synthesized from inorganic compounds. D. Mitochondria possess their own DNA.
d
Which of the following take(s) place during either interphase or mitosis in animal cells? I. Re-formation of nuclear membranes II. Pairing of homologous chromosomes III. DNA replication A. I only B. I and II only C. II and III only D. I and III only
d
List two processes that involve mitosis
growth (through increasing cell number); embryonic development; tissue production/repair;
List two examples of how human life depends on mitosis.
growth/production of (extra) body cells; clonal selection / division of lymphocytes first stage of spermato/oo/gametogenesis
Outline the bonding between DNA nucleotides
hydrogen bonds between nucleotides of opposite strands/complementary bases/adenine and thymine and cytosine and guanine; covalent bonds between nucleotides within strands/between sugar/deoxyribose and phosphate;
Explain how multicellular organisms develop specialized tissues
only some genes are expressed in each cell type/tissue; tissues therefore develop differently/become differentiated;
State two characteristics of stem cells that can be used to distinguish them from other body cells.
retain the capacity to divide; they are undifferentiated
Describe the events that occur during mitosis.
sequence of stages is prophase → metaphase → anaphase → telophase; During prophase the spindle microtubules grow and extend from each pole to the equator. Also chromosomes super coil and become short and bulky and the nuclear envelope breaks down. During metaphase the chromatids move to the equator and the spindle microtubules from each pole attach to each centromere on opposite sides. During anaphase the spindle microtubules pull the sister chromatids apart splitting the centromeres. This splits the sister chromatids into chromosomes. Each identical chromosome is pulled to opposite poles. During telophase the spindle microtubules break down and the chromosomes uncoil and so are no longer individually visible. Also the nuclear membrane reforms. The cell then divides by cytokinesis to form two daughter cells with identical genetic nuclei
Describe how Pasteur's experiments provided convincing evidence to falsify the concept of spontaneous generation.
spontaneous generation is life appearing from nothing / from non-living things. Biogenesis describes the principle that living things only arise from other living things by reproduction (not spontaneous generation). Pasteur falsified this concept through his experiment: Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation) Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur
Describe the importance of stem cells in differentiation
stem cells are undifferentiated cells; embryo cells are stem cells; stem cells can differentiate in many/all ways / are pluripotent/totipotent; differentiation involves expressing some genes but not others; stem cells can be used to repair/replace tissues/heal wounds;
Describe the events that occur in the four phases of mitosis in animals.
supercoiling of chromosomes in prophase; chromosomes consist of sister chromatids in prophase; formation of mitotic spindle / centrosomes/centrioles move away in prophase; nuclear membrane breaks down in (late) prophase/(early) metaphase; attachment of spindle microtubules to centromeres; chromosomes on metaphase plate/equator/centre of cell in metaphase; parting of (sister) chromatids at onset of anaphase; movement of sister chromosomes (accept chromatids) to opposite poles in anaphase; re-formation of nuclear membranes in telophase;
Explain why DNA must be replicated before mitosis and the role of helicase in DNA replication
two genetically identical nuclei/daughter cells formed during mitosis (so hereditary information in DNA can be passed on); two copies of each chromosome/DNA molecule/chromatid needed; helicase unwinds the DNA/double helix; to allow the strands to be separated; helicase separates the two (complementary) strands of DNA; by breaking hydrogen bonds between bases;
State the process that results in tumour (cancer) formation or development.
uncontrolled mitosis/cell division
Outline, with an example, the process of exocytosis
vesicles carry material to plasma membrane; vesicle fuses with membrane; (by joining of) phospholipid bilayers; aided by the fluidity of the membrane; material released/expelled from the cell; membrane flattens; name of example e.g. exocytosis of neurotransmitter / exocrine secretion/ endocrine secretion / hormone secretion
State the role of water in photosynthesis
water molecules undergo photolysis/are split by light energy; forms oxygen as a by-product; hydrogen helps power the fixation of carbon (into organic molecules);
Exceptions to cell theory:
• Skeletal muscles are made of muscle fibres. They are enclosed inside a membrane but are very long and contain lots of nuclei • Giant Algae such as acetabularia can grow up to 100 mm but are unicellular • Aseptate fungi consist of thread-like structures called hyphae. These hyphae are not divided up into sub-units containing a single nucleus. Instead there are long undivided sections o hypha which contain many nuclei
