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B5 Growth and Development – B5.1 How does an organism produce new cells?
1.Why does an organism produce new cells?
All organisms must produce new _______ to grow, repair
damage and to reproduce. All cells start their lives with a
__________ that contains __________ , which are made
from long molecules of ______ . The DNA has a _______
helix structure that allows it to make exact ______ of
itself and provides instructions ( ________ ) so that the
cell can make the right ________ at the right time.
2.Mitosis: Cell division by mitosis produces (four / two) new cells (different / identical) to each
other and to the parent cell. Before mitosis can occur there must be a cell (growth / reduction)
phase when the numbers of organelles in the (cytoplasm / nucleus) increase and the chromosomes in
the (cytoplasm / nucleus) are copied by (four / two) new strands of DNA form alongside them.
Mitosis occurs when the copies of the chromosomes separate and the cell divides into (four / two).
1
New nuclear membranes begin to reform around the
two new nuclei.
2
7
The chromosome pairs separate and move to opposite ends of
the cell.
chromosome
The two identical daughter cells separate from each other.
DNA double helix
The DNA becomes shorter and fatter allowing the
chromosomes to be seen.
3
6
Chromosome pairs line up along the centre of the cell.
The nuclear membrane breaks down so the chromosome pairs
can move around the cell.
Word bank: single, proteins, DNA, genes,
copies, nucleus, double, chromosomes, cells
3.Mitosis:
5
4
1
The parent cell containing DNA spread out in the nucleus.
4.Sexual reproduction and meiosis: Most plants and animals reproduce ____________ . Male and
female sex cells or ___________ join up at ___________. A fertilized egg is called a ________,
which divides to produce the new organism. The zygote contains a set of ____________ from
each parent. The zygote contains instructions for making all the different types of cells in the
organism’s body.
Word bank: zygote, asexually, gametes, chromosomes, sexually, fertilization
1. How many cells above are in the mitotic phase? ….......
2. How many cells above are in the growth phase? ……..…
3. Why must cells divide?
………………………………………………………………………………...……….........
.………………………………………………………………………………………………...
4. What two steps happen during cell growth? ………………..
……………………………………………………………………………………………………..
5. How many cells are made from one parent cell by
mitosis? ………………………………………………………………………………..…..
Gametes contain
only half the number
of chromosomes
compared to body
cells. They are
produced by a
special type of cell
division called
Meiosis. It is
important that the
cells produced only
contain half the
chromosome number
of the parent cell.
Meiosis (MEI) or Mitosis (MIT)?
Complete the diagram of Meiosis by
adding the right number of
chromosomes to the empty dividing cells.
2 cells produced
parent
cell
4 cells produced
chromosomes
duplicate
first
division
second
division
gametes
MIT
New cells are identical
to the parent cell
New cells are used for
growth
New cells contain half the
number of chromosomes
compared to the parent cell.
B5 Growth and Development – B5.2 How do genes control growth and development within the cell?
5.DNA structure and replication:
chromosome
Both strands of the DNA molecule are made
up of 4 different bases, which always pair
up the same way. This is called base pairing.
DNA double helix
T
(1) Base pairing means exact copies of DNA can be made.
(2) Weak bonds between bases split, opening up the
DNA from one end to form 2 strands. Immediately, new
strands form from free bases in the cell. (3) The two
new chains are identical to the original because A always
pairs with T, and G always pairs with C.
(1)
pairs of bases
between two
chains
(2)
(3)
chains made of
deoxyribose (a type of
sugar) and phosphates
Features are passed on from parents to their offspring
because information is carried on the chromosomes.
Chromosomes consist of DNA, which has a double helix
structure (a bit like a twisted ladder).
6.Making proteins
The order of the bases in a gene is the code
for building up amino acids in the correct
order to make a particular protein.
Fill in the correct base pairs
(A,C,G,T)
The genetic code is in the nucleus but proteins are
produced in the cell cytoplasm. Genes do not leave the
nucleus but a copy of the gene, messenger RNA
(mRNA), is produced to carry the genetic code to the
cytoplasm.
Fill in the correct base pairs
(A,C,G,T)
1.
2.
3.
5.
4.
6.
Word bank: nucleus, gene copy is made; amino acids; different; cytoplasm; 3 DNA bases;
amino acids are joined together; gene copy leaves the nucleus;
1. The bases in a DNA molecule always bond in the same
way (4,7)
2. The small molecules that make up proteins (5,5)
3. The division that produces gametes (7)
4. Sex cells (7)
5 A. Messenger RNA (4)
5 D. The division that produces cells for growth (7)
6. A sequence of 3 bases coding for a particular
amino acid in the genetic code (7,4)
B5 Growth and Development - B5.3 How do new organisms develop from a single cell?
7. Making a new human
You began your life as a single cell but now you are made of
millions of cells. Your development has been gradual.
Zygote
(Egg cell fertilized by a
sperm cell)
What are these specialised
cells?
Zygote divides to
develops into a
ball of cells. This
is called the
embryo.
Zygotes divide by (mitosis / meiosis) to form an
embryo. In a human embryo, up to the (4 / 8) cell stage,
all the cells are (different / identical) and could
produce any sort of cell required by the organism.
These are called embryonic stem cells. After this point
the cells become (specialised / unspecialised) and form
(the same / different) types of tissue.
Finish the sentences
The heart and brain in
humans are …..
tissues
Humans have more than
300 different types of
cells, they are …….
specialized
Cells that have
particular functions
are …..
organs
Groups of specialised
cells are called …..
organs
Groups of tissues
are called …..
multicellular
Specialised cells – special proteins
Stem cells
Your body has more than 300 types of cells. Each cell type has its own set of
proteins. Keratin is a structural protein found in hair, skin and nails and it is
strong and insoluble.
Adult and embryonic stem cells have the potential to produce cells needed to
replace damaged tissues. In carefully controlled conditions of mammalian
cloning, it is possible to reactivate inactive genes in the nucleus of a body cell
to form cells of all tissue types.
Although body cells in an organism contain the same genes, many genes in a
particular cell are not active because it only produces the specific proteins
it needs. Genetic switches are used to switch genes on and off.
In the chromosomes above, which would you find in an unspecialised cell? (
Are the genes involved in respiration turned on or off in all cells?
(
Does turning genes off make a cell specialised or unspecialised? (
What do genes give the codes to make?
(
)
)
)
)
Nerve cells
Burns and ulcers
Heart muscle cells
Diabetes
Insulin secreting cells
Parkinson’s disease
Skin cells
Damage caused by heart attack
B5 Growth and Development - B5.3 How do new organisms develop from a single cell?
8. Plant development:
Unlike animal cells some plant cells
remain unspecialised and can
develop into any type of plant cell
Unlike animals, most plants
continue to grow in height
and width throughout their
lives.
Unspecialised cells produce clones of a
plant. You can make from cuttings.
Plant meristems divide to produce
cells that result in increased height
length of roots and girth of plant
New cells in plants specialise into
cells of roots, leaves or flowers
If the hormonal conditions in their environment are changed,
unspecialised plant cells can develop into a range of other tissues or
organs
Explain the diagram above.