2.1 Cell theory
2.1.1 Outline the cell theory
● Living organisms are composed of cells
● Cells are the smallest unit of life
● All cells come from preexisting cells
2.1.2 Discuss the evidence for the cell theory
● Living organisms are composed of cells
○ Observing living things under microscopes reveals cells. Robert Hooke observed cells first when he observed cork under a microscope in 1665.
● Cells are the smallest unit of life
○ No living entity has been discovered that is not made of at least one cell.
○ Experiments have proved that organelles cannot exist outside the cell, meaning cells are the smallest unit of life.
● All cells come from preexisting cells
○ Louis Pastour proved in the 1860s that cells do not appear “spontaneously”. He treated one sample of chicken broth with bacteria and one without --the sample with bacteria flourished with bacteria after some time while the other sample remained sterile.
○ Observation of cells under microscopes show cell division by mitosis and meiosis.
2.1.3 State that unicellular organisms carry out all the functions of life.
2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit.
● cell membrane: 10 nm
● viruses: 100nm
● bacteria: 1 µm
● organelles: up to 10µm
● cells: up to 100µm
2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnifications
2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size.
● The maximum size of a cell is limited by its surface area to volume ratio, which would become too small.
○ Consider the surface area to volume ratio of varying sizes of cubes as an example (a mathematical model using cubes is acceptable in the syllabus):
Dimensions | 1x1x1 | 2x2x2 | 3x3x3 |
Surface area | 6 | 24 | 54 |
Volume | 1 | 8 | 27 |
SA:V ratio | 6/1=6 | 24/8=3 | 54/27=2 |
● The rate at which materials enter or leave a cell depends on the surface area of the cell.
● The rate at which materials are consumed or waste/heat is produced depends on the volume of the cell.
● A cell that is too large may not be able to excrete waste, lose heat or take in essential materials at a high enough rate because the surface area is not large enough to support the volume.
● As a result, the size of a cell is limited by the SA:V ratio.
2.1.7 State that multicellular organisms show emergent properties.
Emergent properties arise from the interaction of component parts: the whole is greater than the sum of its parts.
2.1.8. Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.
● The cells of a multi-cellular organism undergo differentiation and become specialized in both their structure and function. These cells are then organized into tissues and organs.
● Every cell in an organism carry the same genetic information.
● Cells differentiate by expressing some genes but not others
● By differentiating, cells become specialized to carry out specific functions. However many specialized cell lose the ability to perform other functions, such as cell division, such as nerve cells and muscle cells.
2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways.
2.1.10 Outline one therapeutic use of stem cells.
● Hematopoietic stem cells (HSCs) are introduced into humans to replace the damaged bone marrow of some leukemia patients.
● The placenta and umbilical cord of a newborn baby is used as a source of stem cells. Following childbirth, the placenta is drained through the umbilical cord so that cord blood, containing many HSCs, is collected.
● Red blood cells are removed and the remaining fluid is tested to find its tissue type, checked for disease-causing organisms, and stored in liquid nitrogen in a blood bank for cord blood.
● The cord blood is used to treat patients with leukemia. The patient’s tissue type is matched with cord blood in the bank. If suitable cord blood is available, the patient is given chemotherapy drugs that kill bone marrow cells, including the cells causing leukemia.
● The cord blood is taken from the bank, thawed, and introduced into the patient’s blood stream intravenously. The HSCs establish themselves in the patient’s bone marrow, where they divide and differentiate to build the population of bone marrow cells to replace those killed by the chemotherapy drugs.
2.2 Prokaryotic cells
2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote.
The diagram should show the cell wall, plasma membrane, cytoplasm, pili, flagella, ribosomes and nucleoid (region containing naked DNA).
***include pili and flagellum
2.2.2 Annotate the diagram from 2.2.1 with the functions of each named structure.
● Cell wall: a protective outer layer that prevents damage to the cell and prevents the cell from bursting due to internal pressure.
● Plasma membrane: transport of materials in and out of the cell (through pumps and channels) is controlled by the plasma membrane.
● Cytoplasm: contains enzymes which catalyze the reactions of the cell’s metabolism and house the DNA of the cell in a region called the nucleoid.
● Pili: hair-like extensions from the cell wall that can be ratcheted in and out; used for cell-to-cell adhesion, adhering to other surfaces, and to transfer DNA to other cells (conjugation)
● Flagella: solid protein structures with a corkscrew shape, extending from the cell wall; used for locomotion.
● Ribosomes: organelle involved in protein synthesis, which are free floating in the cytoplasm.
● Nucleoid: a region in the cytoplasm where the naked (no histones) circular DNA is located.
2.2.3 Identify structures from 2.2.1 in electron micrographs of E. coli.
2.2.4 State that prokaryotic cells divide by binary fission.
2.3 Eukaryotic cells
2.3.1 Draw and label a diagram of the ultrastructure of a liver cell as an example of an animal cell.
The diagram should show free ribosomes, rough endoplasmic reticulum (rER), lysosome, Golgi apparatus, mitochondrion and nucleus.
pg. 15 of the textbook
2.3.2. Annotate the diagram from 2.3.1 with the functions of each named structure.
● Ribosomes: used in protein synthesis. (Free ribosomes synthesize proteins for use within the cell, not for export)
● Rough endoplasmic reticulum: site of protein synthesis; proteins are transferred to the Golgi apparatus from here.
● Lysosome: single membrane bound sacs which are formed from Golgi vesicles;contain digestive enzymes which are used to break down material (food, other organelles) in the cell.
● Golgi apparatus: stores, modifies, and packages macromolecules (proteins and lipids) which are exported from the cell.
● Mitochondria: the site of cellular respiration
● Nucleus: it is the control centre of the cell and holds its genetic material (DNA).
2.3.3 Identify structures from 2.3.1 in electron micrographs of liver cells.
2.3.4 Compare prokaryotic and eukaryotic cells.
Prokaryotes | Function | Eukaryotes |
Approx. 1-10 µm | Size | Approx. 10-100 µm |
No nucleus present; a circular strand of naked DNA floats within the cytoplasm in a region called the nucleoid. Also smaller segments of genetic material called plasmids are present as loops floating within the cytoplasm. | Genetic material | DNA is housed within the nucleus, which is separated by a nuclear envelope. Multiple strands of DNA are present as chromatin (before replication) in a double-stranded helix, supported by histones. |
A cell wall made of peptidoglygan is present in all prokaryotes. | Cell wall | A cell wall made of cellulose is present in plants. |
Very little or no membrane-bound organelles are present. | Organelles | Organelles with double membranes (mitochondria, nucleus, chloroplast) or single membranes (Golgi apparatus, ER, vacuole, lysosome) |
Uses ribosome 70S; transcription and translation occur simultaneously since DNA is located directly within the cytoplasm. | Protein synthesis | Uses ribosome 80S; transcription occurs in the nucleus while translation occurs in the cytoplasm –the processes are separated by space and time. |
Simple flagellum of approximately 20nm. | Motile organisms | Cilia or larger flagellum of approximately 200nm. |
(From syllabus)
Differences should include:
• naked DNA versus DNA associated with proteins
• DNA in cytoplasm versus DNA enclosed in a
nuclear envelope
• no mitochondria versus mitochondria
• 70S versus 80S ribosomes
• eukaryotic cells have internal membranes that
compartmentalize their functions.
**remember to include similarities as well.
2.3.5 State three differences between plant and animal cells
● One difference is that a plant cell has a cellulose cell wall outside the plasma membrane. It is for the purpose of giving strength and structural support to the cell.
● A second difference is in the vacuoles of plant and animal cells –plant cells have a large, permanent vacuole while animal cells have smaller temporary vacuoles.
● A third difference is that plants have chloroplasts, which are used for photosynthesis and storing starch. Animal cells do not have chloroplasts and do not synthesize sugars or store starch.
2.3.6 Outline two roles of extracellular components.
● The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravity.
● Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhesion and movement.
2.4 Membranes
2.4.1 Draw and label a diagram to show the structure of membranes.
The diagram should show the phospholipid bilayer, cholesterol, glycoproteins, and integral and peripheral proteins. Use the term plasma membrane, not cell surface membrane, for the membrane surrounding the cytoplasm. Integral proteins are embedded in the phospholipid of the membrane, whereas peripheral proteins are attached to its surface. Variations in composition related to the type of membrane are not required.
pg. 21 in textbook
2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.
● Water is a polar molecule, and therefore attracts other polar molecules while repelling non-polar molecules.
● The phosphate head of a phospholipid molecule is hydrophilic because it is polar.
● The fatty acid tails of a phospholipid molecule is hydrophobic because it is non-polar.
● In water phopholipids always form a bi-layer, where the hydrophilic phosphate heads are oriented towards water and the hydrophobic fatty acid tails are oriented away from the water and towards the centre.
● This arrangement is found in biological membranes.
● Since the hydrophobic tails do not strongly attract each other, the bi-layer is fluid. The attraction of the hydrophilic heads to the water makes for a very stable structure.
2.4.3 List the functions of membrane proteins.
Include the following: hormone binding sites, immobilized enzymes, cell adhesion, cell-to-cell communication, channels for passive transport, and pumps for active transport
2.4.4 Define diffusion and osmosis.
● Diffusion is the passive movement of particles from a region of high concentration to a region of lower concentration, as a result of the random movement of particles.
● Osmosis is the passive movement of water molecules from a region of low solute concentration to a region of higher solute concentration, across a partially permeable membrane.
2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion.
● Simple diffusion
○ Simple diffusion involves the movement of particles between the phospholipid molecules in the membrane.
○ The phospholipid bi-layer is non-polar through the centre. This means that non-polar molecules and uncharged particles can pass through the membrane more easily that particles with charge.
○ Small particles pass through more easily than larger ones.
○ Movement occurs across a gradient (concentration, electrochemical, etc): from an area of higher concentration to an area of lower concentration. Movement is therefore passive.
● Facilitated diffusion
○ Facilitated diffusion involves the movement of particles through a protein channel.
○ Charged particles and molecules, which cannot pass through the non-polar bi-layer, use facilitated diffusion.
○ The use of channels allows a cell to control the substances that enter and exit it.
○ Channels are specific to the particles that they allow to pass.
○ Movement occurs across a gradient (concentration, electrochemical): from an area of higher concentration to an area of lower concentration. Movement is therefore passive.
○ Water is a polar molecule and moves through facilitated diffusion through channels and this is known as “osmosis”.
● Example: sodium and potassium channel proteins in the membrane of neurons which open and close depending on the voltage across the membrane.
2.4.6 Explain the role of protein pumps and ATP in active transport across membranes.
● Active transport involves the movement of particles against a concentration gradient.
● Protein pumps, which are specific to particular substances, are used and this allows cells to control what is absorbed or expelled from the cell.
○ What substance is allowed to pass is determined by the specificity of the binding site in the pump. The substance enters from the side with a lower concentration.
● Active transport requires energy, which is provided by ATP.
○ ATP causes the shape of the pump to change, allowing the release of the substance to the other side of the membrane. Once the substance is released, it changes back to its initial shape.
● Pumps only work in a specific direction.
2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus, and plasma membrane.
● Vesicles are created by the pinching of membranes, which is possible due to the fluidity of membranes.
● Proteins formed at the rough endoplasmic reticulum (rER) are carried to the Golgi apparatus by vesicles. Membrane from the cisternae of the rER is pinched off to create a vesicle and the protein is carried within, which is subsequently fused to cisternae of the Golgi apparatus. Vesicles then carry the proteins from the Golgi apparatus to the plasma membrane.
● Fusion of vesicles to the plasma membrane allow for materials (solid or liquid) to be secreted from the cell.
2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.
● In endocytosis, a small region of the membrane is pulled from the rest of the membrane towards the inner surface of the membrane (into the cell), and then it is pinched off. Contents are enclosed within the vesicle.
○ If solid matter is present in the vesicle, this is “phagocytosis”.
○ If only liquid is present in the vesicle, this is “pinocytosis.”
● In exocytosis, a vesicle containing some material fuses to the plasma membrane, which releases the material to the outside of the cell.
2.5 Cell division
2.5.1 Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis.
● Interphase
○ G1: is a period of growth, DNA transcription and protein synthesis
○ S: is a period of DNA replication
○ G2: is a period of preparation for division
● Then mitosis occurs, where the nucleus divides to form two genetically identical nuclei.
● The cytoplasm divides through cytokinesis.
● (The two cells enter interphase when cytokinesis is complete)
2.5.2 State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue.
2.5.3 State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.
2.5.4 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).
● Prophase
○ chromosomes become shorter and fatter by supercoiling
○ the nuclear membrane breaks down
○ spindle microtubules begin to grow and are complete by the end of prophase
○ centrosomes move to opposite poles of the cell
● Metaphase
○ the chromosomes line up across the equator of the cell (metaphase plate)
○ the spindle microtubules attach to the centromeres of each pair of chromatids
● Anaphase
○ the centromeres are divided and the chromatids become chromosomes
○ the spindle microtubules pull the chromosomes to opposite poles
● Telophase
○ the chromosomes have reached opposite poles and nuclear envelopes begin to form around them
○ chromosomes uncoil to chromatin
○ the cell elongates in preparation for division (cytokinesis)
2.5.5 Explain how mitosis produces two genetically identical nucleus.
● exact copies of each chromosome are made during replication during interphase, when sister chromatids are formed.
● chromatids remain attached by their centrometres during metaphase of mitosis, when they are lined up at the metaphase plate and attached the spindle fibres at opposite ends of the cell.
● centromeres then divide during anaphase to opposite poles, therefore one copy of each chromosome moves to each pole of the spindle.
● the chromosomes at the poles form the new nuclei
● cells are then formed after cytokinesis, each with an exact copy of the original nucleus
2.5.6 State that growth, tissue repair, and asexual reproduction involve mitosis.
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