Download Cell division and Survival

Cell division and Survival
Reproduction of cells is essential if an organism is going to grow, repair itself and replace cells that
have died. As far as the species is concerned it is even more essential that the organism replaces
itself with a younger replacement.
1. Cells of Producers (plants) and Consumers (animals) are similar in many respects. Label the
organelles in the two types of cells below and answer the questions that follow.
green c___________________
c______ w_______
cy____________
m________________
n_________
containing
ch____________
_
large
v__________
__
c_____
m__________
What are the three organelles plant cells have, that animal cells do not?
i)_____________________ ii)__________________________
iii)______________________
2. Fill in the gaps in the following sentences explaining where genes
are and cell division by Mitosis.
The n____________ is the control centre of the c_______. It contains
ch______________ which carry on them all the instructions for how to
make the complete organism. The instructions are written in a code as
A single gene on a length
of chromosome ( a bit of
DNA)
individual g_________. There are actually two sets of instructions (two
sets of c______________) in every cell in an organism (two sets of
g________). One set came from the m_______ parent and one set
came from the f________ parent. All organisms start off with a single
cell that divides again and again to grow a complete individual.
Single cell with
two sets of
chromosomes
in its nucleus
Both sets of ch____________ need to be
co___________ exactly into every n_____ c___ or
the cells would not know how to do what they
were supposed to do. The process of making an
exact c__________ of a cell is called M_______.
Two identical cells are made from one cell and genetic material (the
ch___________ and the g___________ that make them up) are
exactly the same as the single cell that d_________ by M_________
Two identical cells
produced by
Mitosis cell division
Asexual Reproduction –reproduction without sex
Because every cell in an organism contains a complete set of genetic instructions on how to make
the entire organism you can grow one exactly the same from a single cell (this is called cloning).
However it is easier to do it from a whole group of cells. Because you are reproducing a new
organism without sex it is called asexual reproduction.
Plants and some animals (aphids) naturally reproduce asexually.
1. Label the following diagrams of plants that naturally use asexual reproduction to colonise an area
of ground.
Clover Plants
Twitch grass
Potato plants
Pa_________
plant
St_______
above
ground
Pa_________
plant
identical
cl_____
of plant
Rh______
below
ground
Pa_________
plant
identical
cl_____
of plant
T_______
identical
cl_____
of plant
2. Man also uses the method of asexual reproduction to mass produce plants which grow up
identical to their parents. They are the same plant simply growing on a different set of roots. Label
the following diagrams and complete the sentences below showing how cuttings are made.
Axial Bud
A branch of a plant
that is required to be
a______________
r_____________ is
chosen and a small
length is cut off that
contains a growing
m___________, an
ax________ bud and
a couple of le______.
The c__________
has exactly the same
g________ in every
cell’s n___________
as the parent plant it
was taken from. It will
grow up looking
exactly the same
because it is a
c_________.
The cutting must
make
ad_______________
r___________ on its
stem if it is going to
suck up water and
minerals to survive. It
is placed carefully in
damp sand to allow
for these roots to
develop.
The c___________
has a plastic bag
over the whole pot to
prevent the cutting
losing too much
water before it has
grown it’s
a________________
r_________ and is
able to survive as a
separate new
identical c________
of the parent plant.
Advantages and Disadvantages of Asexual Reproduction
1. Examine the drawing above and complete the following sentence.
Because all c__________ have exactly the same g_________ on their ch_____________
the major disadvantage of a_______________ r
is that any disease or climatic
event that kills one individual will kill them all.
2. Examine the drawing above and complete the following sentence.
If the individuals do not have the same g_________ on their ch_______________ some will survive
to reproduce and the species will carry on in a modified way. This is the basis of Evolution –
selection by survival of the fittest.
3. Natural and artificial asexual reproduction is not all bad. There are significant advantages as
well.
The top line of trees were all produced using
asexual reproduction by growing cuttings. As
a forest grown for logs and timber, state two
advantages and one disadvantage these
trees would have over the bottom row which
were not genetically identical.(seed grown)
Ai)______________________
________________________
Aii)______________________
________________________
Di)_______________________
________________________
4. Complete the following sentence to revise the other major advantages of
asexual reproduction.
If the growing season is shortened by a long winter, or if there are no pollinating
insects, if there is only a single individual left, it cant do sexual r______________ The
The individual can still do a___________ r___________ and the species
su_____________ for another year and colonises the area of ground,
keeping out competing plants.
Sexual Reproduction using Meiosis
Sexual reproduction produces a new individual that is different from its parents. Every cell has two
sets of chromosomes (Diploid 2n). One set came from the female parent and one set came from
the male parent. The single sets have to be packaged in a single cell as a gamete (Haploid n ).
Meiosis is the cell division that enables these packages (gametes) containing a single set of
chromosomes to be made from cells that contain two complete sets of chromosomes.
1. Complete the following sentences that explain the
diagram on the right.
2n
2n
The female body cell has two complete sets of two
ch______________. It is a d_________ cell (2n)
because it contains two sets of two chromosomes.
n
n
n
n
One set came from her m___________ and one set
n
came from her f_________. Organisms have different
n
numbers of ch__________ that make up a complete
set. Humans have two sets of 23 ch_____________.
n for humans is therefore 23. Every d____________
cell in a human has 46 ch_____________. Gorillas
have two sets of 24 chromosomes (n= 24) so every
gorilla body cell has 48 chromosomes. The diploid cell
d_________ by M_________ to form g___________
that contain only o______ set of ch_____________.
These are called h___________( n) cells. Notice that
the female gamete in this case has o________ set of
two chromosomes. The same M__________ cell
division occurs in the male d_________ cell. The male
cell produces h___________ g___________ that
contain only one set of ch______________.
The two gametes fuse together in a process called
f__________________. This results in a cell called a
z__________. The z__________ contains the
required two sets of c_______________ and is
d_____________. This cell then divides by mitosis
and a new genetically different individual grows. The
start of a new life!
Gametes form
in the ovaries
of women and
the testicles of
men.
Single celled
Zygote
formed from
fertilisation
2n
Answer the following questions
about the diagram above.
2. How many complete sets of
chromosomes did each parent
have? ___________
3. How many complete sets of
chromosomes do the gametes
have? ___________
4. How many complete sets of
chromosomes does the fertilised
zygote have? ___________
5. How many chromosomes make
up one set in this species of cell?
6. What is the n number in the cells
above? ___________
7. n is 23 in humans . How many
individual chromosomes are there
in every body cell? _____
8. How many individual
chromosomes are there in each
gamete? ___________
9. How many individual
chromosomes are there in a
fertilised zygote? _________
Mendelian Genetics and Punnett Squares
All body cells are diploid (have two complete sets of chromosomes). They therefore contain two
genes (two sets of instructions) for everything the organism looks like and does. All gametes are
haploid because they only contain one set of chromosomes. The gametes therefore must contain
only one complete set of genes each. When gametes from two different parents fuse by fertilisation
the zygote again becomes diploid and has two sets of instructions (genes). A punnett square is a
simple device to look at the likely outcomes from a mating of two different individuals. The genes
are given single letters and there are always two letters (signifying diploid) given for each parent
e.g. TT, Tt or tt.
Female parent
T = Dominant gene = Tall
t = Recessive gene = short
Tall
Gametes
Gametes
Male parent
Tt
T
t
T
TT
Tt
Phenotype
t
Tt
tt
Genotype
Offspring
Tt
Tall
¾ tall
¼ small
¼ TT
½ Tt
¼ tt
1. Complete the table linking the scientific term with its correct definition (arrow) and write in the
letter, letters or words from the diagram above that correspond with the definition
(one has been done for you).
Scientific Term
Definition
Dominant gene
is two letter shorthand for the combination of
Genes in every cell of the organism the zygote
grows into. The dominant gene is always written
first.
is written with a capital letter and as the name
suggests is the set of instructions the zygote cell
uses to make something look the way it does
Recessive gene
Phenotype
Genotype
Homozygous
Heterozygous
Gamete
is when both the genes in every cells nucleus are
the same.
(Hint think homosexual = likes the
same sex)
is a fertilised egg (the first diploid cell made when
two gametes fuse ).
is written with a small letter. This gene will never
be used as a set of instructions to change its
looks unless the zygote cell has no alternative.
The cell produced by meiosis that is haploid
(contains only one set of chromosomes) eg
sperm, egg, ovule, pollen.
is the Physical expression of the gene (what the
zygote looks like when it has grown up).
Letter, letters or
words
__
__
__
_
TT
tt
__
__
__
__
_
_
______
Zygote
is when both the genes in every cells nucleus are
different. (Hint think heterosexual = likes the
different sex)
__
Punnett Square practice
1. Complete the following sentences.
These two plants are both peas. They look Physically
different because the P______________ of the one on
the left is short and the p______________ of the one on
the right is tall. The tall p________________ plant must
have at least one d__________ gene in its
g_____________. It would therefore be either T t or _ _.
The tall plant therefore can be either Tt which is called h______________ or TT
called h_____________ d______________. The short _______________ plant
can not have a dominant gene in it so it must have a g_____________ of _ _.
This genotype is called ho_________________ r__________________.
Gametes
2. If these two plants are crossed the gametes they produce will be transferred
as pollen and fertilise the ovules of the other plant. The zygote that develops from the fertilised
ovule grows into a seed that would then grow into an offspring pea plant. Complete the Punnett
squares below and predict both the fraction split for genotype and phenotype as was done on the
previous page.
a)
Female
TT
Tall
parent
T = Dominant gene = Tall
Gametes
t = Recessive gene = short
T
T
Offspring
T
Male parent
Phenotype
all _____
___ Short
Genotype
½ TT
___ _____
Tt
t
Tall
b)
Female parent
T = Dominant gene = Tall
t = Recessive gene = short
Tt
Tall
Gametes
Gametes
Offspring
Phenotype
Male parent
Short
tt
Genotype
___ _____
___ _____
___ _____
___ _____
___ _____
Sex determination in Humans
The sex of a zygote, that grows into a baby and then into one of
us, is determined not by a single gene on a chromosome but by
the length difference of an entire pair of chromosomes The sex
chromosomes are called X and Y. Hint Looking at the letters Y is
simply an X that has lost a bit. The Y chromosome has lost a bit
and is shorter than the X chromosome) XX zygote cells are
female. One of the X chromosomes still came from the mother of
the girl zygote and the other X chromosome came from her dad.
XY zygote cells are male. The X chromosomes came from the
mother of the boy zygote and the Y chromosome came from his
dad.
The sex of a baby is therefore determined by which sperm gamete
wins the race. One containing a short Y chromosome will fertilise
the egg and make the zygote a boy. If a sperm gamete wins that
contains the longer X chromosome a girl zygote will be made.
XX
From
their
Mum
XY
From
their
Dad
1.Complete the Punnet Square below for sex determination in humans. and fill in the Offspring table
showing fractions as usual.
Female parent
gametes
X = long chromosome = female
Y = short chromosome = male
XX
tall
gametes
Offspring
Phenotype
___ _____
___ _____
genotype
___ _____
short
___ _____
___ _____
We all know there is a girl out there just waiting for us (and a boy if you are a girl) and the Punnet
Square predicts that half the babies born will be female XX and half XY.
Male parent
XY
The Punnet Square Offspring box therefore predicts the proportions of likely numbers of different
phenotypes that will occur in a population. eg 50% male : 50% female.
2. Complete the following sentences.
The major advantage in s_______ reproduction by m___________ is that there is va__________
in p________________ ( what the offspring look like) and g______________ (what their two sets
of g_______ are). Because they are dif_________ from their parents that d___________ may
allow that individual a comparative advantage so it has a greater chance of r___________ and
passing on its g___________ to its offspring. In the picture below the white flowers were all killed
which left the dark flowers to breed and the dark coloured flowers took over. Evolution- survival
of the fittest works in this way.
3. Write a short statement about what happened to the mouse population.
_________________________
_________________________
_________________________
_________________________
_________________________