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IB Biology
2.1.1
Student Work Book
Topic 2: Cells
The Cell Theory Debate-
Homework
When there is evidence to disprove a theory scientists have to start doubting the theory.
This is particulary difficult to do when the theory has obvious uses, and if the theory has
been accepted for a long time. Cell theory is an example of a theory where it can be
applied to nearly all organisms but with a few specific exceptions.
Should we abandon the theory?
Make a four slide presentation
a) what are the key points of ‘cell theory’?
b) describe the evidence that supports it?
c) what examples of cells are there which don't support it.
(ie; fungal hyphae, skeletal muscles, amoeba)
d) Explain whether we should keep the cell theory or change it?
Essential Content for the presentation
Include the following evidence.
Outline the cell theory.
2
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Living organisms are composed of cells.
Cells are the smallest unit of life.
Cells come from pre-existing cells.
TOK: The accumulation of evidence allows a Scientific hypothesis to become a
Discuss the evidence for the cell
theory. Deciding whether a theory should be abandoned when there is evidence
3
theory.
that it does not offer a full explanation requires NEW EVIDENCE…the
question is ‘How much?”
This is evidence that contradicts Cell theory –
State that unicellular organisms
1
carry out all the functions of life. These organisms are not made of cells, their bodies are not subdivided. The cell
is an organism capable of metabolism, response, homeostasis, growth,
reproduction and nutrition.
Extra cellular components are
not part of the
cell.
Outline two roles of extracellular components. (these are useful to cells but not
part of the cell........
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.
2.1.6 Surface Area to Volume Ratio - Homework Sheet
1. Rank the following cells from smallest to largest in terms of surface area to
volume ratio. Give reasons for the rankings you decide upon. (2 marks)
2. Why is a large surface area to volume ratio useful to a functioning cell? (1 mark)
3. Complete the following table that describes the dimensions of cube-shaped cells.
All sides are of equal lengths (X) with surface area equal to (X squared) x 6 and
volume equal to X cubed. (3 marks)
4. As cells increase in size the surface area to volume ratio ( increases / decreases ).
What does this mean for the cell if it can only exchange nutrients and wastes at
the cell membrane? (2 marks)
2.2
Prokaryotic cells
Homework Sheet
1 hour
Bacteria exist in three different shapes, coccus (round), spirilla (spiral), and baccilla (rod).Bacteria are very
small, and with the exception of ribosomes, do not contain cellular organelles. They do have
chromosomes, contained in a nucleoid region, which has no nuclear envelope. Because of this, bacteria are
said to lack a nucleus – this gives them the name ‘prokaryotic’ – “before the nucleus”. Many bacteria have
rings of DNA outside the nucleoid, called plasmids.
1.
Match the descriptions and functions to the Bacteria structures in the table
below – using numbers, lines, or cut&paste.
2.
Bacteria Structure
Description and Function
Capsule
Ring of DNA, contains a small number of genes which typically
provide a selective advantage in a given environment. (eg antibiotic
resistance).
Cell Wall
Protective covering made up of polysaccharides (complex sugars).
Keeps the bacteria from drying out and protect it from being engulfed
by larger microorganism.
Cytoplasm
Gives cell its shape and surrounds the cytoplasm protecting it from the
environment.
Flagella
A layer of phospholipids and proteins, which allows certain materials in
and out of the cell
Nucleoid
Only type of cell organelle found in bacteria. Small structures that
translate the genetic code and synthesise proteins.
Pili
Small hair like projections that emerge from the cell membrane. These
help the bacteria attach to their host.
Plasma Membrane
This is where the functions of cell growth, cellular metabolism and
replication are carried out. It is a gel like material that is composed of
water, enzymes, nutrients, wastes, and gases and contains cell structures
such as the ribosomes, chromosomes, and plasmids.
Plasmid
A region of the cytoplasm where the chromosomal DNA is located.
Ribosomes
Hair like structures that provide locomotion. Not all bacteria have them.
Colour the descriptions RED and the functions BLUE
2.3
Eukaryotic cells Stucture and Function -
Homework Sheet
-
1. Use a pencil line drawing to sketch out an animal cell. Include as many
organelles as possible and label them. (5 marks)
2. Identify the function of each of the following cell organelles in the single line
provided. (6 marks)
Nucleus__________________________________________________________
Cell Membrane ____________________________________________________
Mitochondria ______________________________________________________
Endoplasmic Reticulum ______________________________________________
Ribosomes ________________________________________________________
Golgi Bodies ______________________________________________________
3. Where is the nucleolus located in the cell?
What molecule does the nucleolus produce and what is the function of this molecule?
(3 marks)
4. Where in the cell are vacuoles located and what do they transport?
How is a vacuole different from a vesicle? (3marks)
5. How is the structure of a lysosome related to its function?
Why might they be called “suicide sacs”? Hint – autodigestion. (3 marks)
6. What are the structural and functional differences between rough ER and smooth
ER?
Why do cells of the testes and adrenal glands have large amounts of smooth ER? (3
marks)
7. What is the advantage to the cell of having different organelles that carry out
specialized functions? Explain. (3marks)
8. What happens during the process of cell differentiation? (2 marks)
Membranes
Cell Division