Download Unit 2

CELL
Unit 2
LEARNING AIMS
By the end of this unit students should
– understand basic terms connected with cells and cell division
– be able to use this vocabulary in context
– describe the process of cell division in their own words
KEY WORDS
cell, cell division, cell membrane, chloroplast, chromosome, meiosis, mitochondrion, mitosis, nucleus, reticulum,
ribosome, stem cell, vacuole
LEAD IN
What are cells and how do they work?
Name some differences between animal and plant cells.
What do you know about cell division? Can you describe it?
EX 1
Work in pairs. Look at the differences between animal and plant cells below. Try to fill in the words
animal (A) or plant (P) in the blanks where they belong.
I. __________ cells have strong cell walls made of cellulose, while ____________ do not.
II. Vacuoles in ________________ cells are small and temporary, while __________ cells have a large
permanent vacuole containing cell sap.
III. ___________ cells may contain chloroplasts containing chlorophyll for photosynthesis. ______________
cells never contain chloroplasts.
IV. ____________ cells store energy as starch but ______________ cells store energy as granules of glycogen.
EX 2
Which of these words refer to animal cells, which refer to plant cells and which refer to both?
Cell membrane; Cell wall; Centriole; Golgi apparatus; Chloroplast; Mitochondrion; Nucleus; Ribosome;
Endoplasmic reticulum; Vacuole
Animal cell
Both
Plant cell
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EX 3
Study the pictures below. Decide which of these cells is a plant cell and which is an animal cell.
______________________
___________________________
Use the terms from ex.2 to describe both plant and animal cell.
EX 4
Talk to a partner and discuss the following questions:
1. Why do cells divide?
2. How do cells divide?
EX 5
Read the text and fill in the gaps with the correct words – mitosis or meiosis.
Cell division
Cells divide in two different ways, by mitosis and meiosis. __________ is the kind of cell division that occurs
during growth and asexual reproduction. __________, on the other hand, takes place during the formation of
eggs and sperms. The chromosomes behave differently in these two types of cell division.
__________
The parent cell has four chromosomes: two long ones and two short ones.
Before the cell starts to divide, each chromosome produces an exact copy or replica of itself. The original
chromosome and its replica are called chromatids, and they are held together by a structure called the centromere.
The chromatids now line up across the middle of the cell. Then they part company and move to opposite ends of
the cell. Finally the cell splits across the middle, and the chromatids become chromosomes of the daughter cell.
We now have two cells each of which contains the same number of chromosomes as the parent cell.
__________
The parent cell has four chromosomes.
The chromosomes form chromatids which line up across the middle of the cell – homologous chromosomes
come together and arrange themselves across the middle of the cell, then they part company and move to
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opposite ends of the cell which starts to split into two. There now follows a second cell division in which the
chromatids part company. So, there are two cell divisions, one after the other, and the chromosomes behave in
such a way that the daughter cells have half the number of chromosomes present in the original parent cell.
A cell which has only half the full number of chromosomes is described as haploid; a cell with the full number of
chromosomes is described as a diploid. Cells formed by meiosis are always haploid.
EX 6
Match the words and definitions below.
1. Chromosome
a) describing a nucleus, cell ,or organism with a single set of unpaired chromosomes
2. Chromatid
b) describing a nucleus, cell, or organism with two sets of chromosomes
3. Cell division
c) any of several threadlike bodies, consisting of chromatin, that carry the genes in
a linear order
4. Mitosis
d) the formation of two or more daughter cells from a single parent cell
5. Meiosis
e) either of the two daughter strands of a replicated chromosome that are joined by
a single centromere and separate during cell division to become individual
chromosomes
6. Haploid
f) a type of nuclear division that gives rise to four reproductive cells each with half
the chromosome number of the parent cell.
7. Diploid
g) a type of nuclear division that results in two daughter cells each having a nucleus
containing the same number and kind of chromosomes as the mother cell
EX 7
Underline keywords in the text. When you have finished, copy them on a separate sheet of paper. Try to
explain the process of cell division to your partner but do not look at the text. You may use only the
keywords and the pictures below.
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EX 8
You are going to listen to a presentation on stem cells. First discuss with a partner what stem cells are.
How are stem cells different from other cells?
EX 9
Listen and circle the correct answer.
1. Stem cells are
a) specialized cells.
b) unspecialized cells.
2. Scientists work with
a) two types of stem cells.
b) four types of stem cells.
c) a lot of types of stem cells.
3. Stem cells from human embryos were isolated
a) 20 years ago.
b) in 1998.
c) have not been isolated yet.
4. Stem cells
a) help to treat Parkinson’s disease.
b) are used for treating diabetes.
c) might be useful for treating diseases in the future.
5. Scientists
a) have learnt all they need to know about stem cells.
b) need to learn a lot more information about stem cells
c) will never understand stem cells completely.
EX 10
Choose one of the following statements and explain why you agree with it.
o
o
o
Stem cells have great potential and stem cell research is beneficial.
Stem cell research is beneficial but there are some ethical concerns.
People should not interfere with nature.
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