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IB Biology IB Questions Review questions with correct answers - SL
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IB Biology IB Questions Review questions with correct answers - SL
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IB Biology IB Questions Reviewquestions with correct answers - SL
Outline the cell theory - .......🔷ANSWERS🔶......✔✔ 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
Discuss the evidence for the cell theory - .......🔷ANSWERS🔶......✔✔ Microscopes:
-Microscopes have increased man's ability to visualise tiny objects
-All living things when viewed under a microscope have been found to be made of cells and cell
products (e.g. hair)
-Note: Certain types of cells do not conform to the standard notion of what constitutes a cell
--Muscle cells contain multiple nuclei
--Fungal hyphae consist of multiple cells that share a continuous cytoplasm
Experimental Evidence:
-Cells removed from tissues can survive independently for short periods of time
-Nothing smaller than a cell has been found to be able to live independently
-Experiments by Francesco Redi and Louis Pasteur have demonstrated that cells cannot grow in
sealed and sterile conditions
What functions must unicellular organisms carry out? - .......🔷ANSWERS🔶......✔✔ Unicellular
organisms are the smallest organisms capable of independent life.
All living things share 7 basic characteristics:
-Movement: Living things show movement, either externally or internally
-Reproduction: Living things produce offspring, either sexually or asexually
-Sensitivity: Living things can respond to and interact with the environment
,-Growth: Living things can grow or change size / shape
-Respiration: Living things use substances from the environment to make energy
-Excretion: Living things exhibit the removal of wastes
-Nutrition: Living things exchange materials and gases with the environment
Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and
cells, using appropriate SI units - .......🔷ANSWERS🔶......✔✔ A molecule = 1 nm
Cell membrane thickness = 7.5 nm
Virus = 100 nm (range: 20 - 200 nm)
Bacteria = 1 - 5 um
Organelles = <10 um
Eukaryotic cells = <100 um
Calculate the linear magnification of drawings - .......🔷ANSWERS🔶......✔✔ Magnification = Size
of image (with ruler) ÷ Actual size of object (according to scale bar)
Actual size = Size of image (with ruler) ÷ Magnification
Explain the importance of the surface area to volume ratio as a factor limiting cell size
- .......🔷ANSWERS🔶......✔✔ -The rate of metabolism of a cell is a function of its mass / volume
-The rate of material exchange in and out of a cell is a function of its surface area
-As the cell grows, volume increases faster than surface area (leading to a decreased SA:Vol ratio)
-If the metabolic rate is greater than the rate of exchange of vital materials and wastes, the cell will
eventually die
-Hence the cell must consequently divide in order to restore a viable SA:Vol ratio and survive
-Cells and tissues specialised for gas or material exchange (e.g. alveoli) will increase their surface
area to optimise the transfer of materials
State that multicellular organisms show emergent properties - .......🔷ANSWERS🔶......✔✔
Emergent properties arise from the interaction of component parts: the whole is greater than the
sum of its parts
,Multicellular organisms are capable of completing functions that individual cells could not
undertake - this is due to the interaction between cells producing new functions
In multicellular organisms:
Cells may group together to form tissues
Organs are then formed from the functional grouping of multiple tissues
Organs that interact may form organ systems capable of carrying out specific body functions
Organ systems carry out the life functions required by an organism
Explain that cells in multicellular organisms differentiate to carry out specialised functions by
expressing some of their genes and not others - .......🔷ANSWERS🔶......✔✔ -All cells of an
individual organisms share an identical genome - each cell contains the entire set of genetic
instructions for that organism
-The activation of different instructions (genes) within a given cell by chemical signals will cause it
to differentiate from other cells like it
-Differentiation is the process during development whereby newly formed cells become more
specialized and distinct from one another as they mature
-Active genes are usually packaged in an expanded and accessible form (euchromatin), while
inactive genes are mainly packaged in a condensed form (heterochromatin)
-Differentiated cells will have different regions of DNA packaged as heterochromatin and
euchromatin depending on their function
State that stem cells retain the capacity to divide and have the ability to differentiate along different
pathways - .......🔷ANSWERS🔶......✔✔ Stem cells are unspecialized cells that have two key
qualities:
1. Self renewal: They can continuously divide and replicate
2. Potency: They have the capacity to differentiate into specialised cell types
, Outline one therapeutic use of stem cells - .......🔷ANSWERS🔶......✔✔ Stem cells can be derived
from embryos or the placenta / umbilical cord of the mother; also minimal amounts can be
harvested from some adult tissue
Stem cells can be used to replace damaged or diseased cells with healthy, functioning ones
This process requires:
-The use of biochemical solutions to trigger differentiation into desired cell type
-Surgical implantation of cells into patient's own tissue
Suppression of host immune system to prevent rejection of cells
-Careful monitoring of new cells to ensure they do not become cancerous
Examples of therapeutic uses of stem cells:
1. Retinal cells: Replace dead cells in retina to cure diseases like glaucoma and macular degeneration
2. Skin cells: Graft new skin cells to replace damaged cells in severe burn victims
3. Nerve cells: Repair damage caused by spinal injuries to enable paralyzed victims to regain
movement
4. Blood cells: Bone marrow transplants for cancer patients who are immuno-compromised as a
result of chemotherapy
Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a
prokaryote. Describe the function of each of the named structures. - .......🔷ANSWERS🔶......✔✔
>Pili: Hair-like extensions found on bacteria which can serve one of two roles
>Cytoplasm: Fluid component which contains the enzymes needed for all metabolic reactions
>Cell membrane: Semi-permeable barrier that controls the entry and exit of substances
>Flagellum: Long, slender projection containing a motor protein which spins the flagella like a
propellor, enabling movement
>Ribosome (70s): Complexes of RNA and protein that are responsible for polypeptide synthesis
>Nucleoid: Region of the cytoplasm which contains the genophore (the prokaryotic DNA)
>Cell wall: A rigid outer layer made of peptidoglycan that maintains shape and protects the cell from
damage or bursting if internal pressure is high
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