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S3 Cells, cell uses and DNA
Revision summary
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Animal and plant cells
Cells are the basic units of ______. All living organisms contain cells. There are many different types of cells.
Unicellular organisms are made up of just one cell. Multicellular organisms are made up of many cells.
Cells can be stained to see cell structures more clearly. Examples of stains are ________ solution and methylene
blue.
Parts of the cell and what they do.
Structure
Function (what they do)
Controls what enters and exits the cell
Nucleus
Vacuole
Site of biochemical reactions
Contains watery cell sap to help maintain cell shape
Site of photosynthesis
Cell wall
Cell division
Cell division is when a parent cell divides to produce two ___________ daughter cells.
Cell division is essential for _________. Cell division enables damaged tissues to mend. Unicellular organisms
require cell division for reproduction.
Uncontrolled cell division causes ________
During cell division the genetic material in the nucleus is
replicated (copied). The nucleus divides into two and each
new _________ cell gets a copy. The cytoplasm divides into
two, and a ___________ forms around each cell. The two
new daughter cells need an exact copy of the ______ so they
can function correctly.
Division of the cell to make two identical daughter cells is called __________
WORDBANK: cancer, daughter, DNA, growth, identical, iodine, life, cell membrane, mitosis, cytoplasm,
chloroplast, membrane
The nucleus and cell division
The nucleus contains thread-like structures called ____________.
Chromosomes contain important genetic information.
The characteristic number of chromosomes that certain organisms should have is
called the “Chromosome ______________”
During cell division the chromosomes are visible as double strands because
they have replicated. Each strand is called a ___________.
After lining up along the equator of the cell, these chromatids are separated.
Chromatids are pulled to opposite poles (ends) of the cell by _________ _________
If the daughter cells did not have the same number of chromosomes as the parent cell they would not be able to
perform the same function
Chromosomes
Chromosomes are thread-like structures that carry
________ information.
You will see chromosomes represented in both these ways.
Genes
A gene is a section of a chromosome which contains a separate piece of genetic
information.
A single chromosome contains thousands of different genes.
Each gene codes for a protein e.g. enzymes, hormones & muscle fibres
DNA
DNA stands for DeoxyriboNucleic Acid. Chromosomes and their genes are made of DNA.
Each chromosome is a very long __________ of tightly coiled DNA.
DNA carries the ______ that controls what your cells are made of and what they do.
WORDBANK:
chromatids, chromosomes, code, complement, genetic, molecule, spindle fibres
DNA Structure
DNA is made of a backbone of sugars and _________ molecules. The central link is formed by ________.
The 4 base molecules are adenine (A), cytosine (C), ________ (G), thymine (T).
These bases always pair up in the same way as complimentary pairs, A with T and G with C.
The bases interact to form a ‘twisted ladder’ shape known as the _________ ________.
There are only 4 bases in DNA but they are very important.
The order of just these 4 bases codes for every part, and kind, of life!
Protein formation
DNA contains the __________ instructions to make protein. It carries these instructions in a code of 4 bases.
A sequence of three bases that codes for one _______
_______. These three bases are called _______.
The order of the triplets determines the amino acid sequence.
__________ are made from amino acids joined in long chains.
Amino acids are put in the right place in a protein because of the three base code.
Peptide Bond
The amino acids are held together by special bonds called _________ bonds
Picture of a short amino acid chain
Each _______ contains the sequence of bases for one protein.
Amino acid
Mutations
A mutation is a change in the __________ of bases in DNA. They can be caused by ________ in copying DNA
or the effects of _________ and heavy metal ions. A DNA mutation changes the base sequence.
This can change the amino acid sequence and so a different __________ may be produced.
If incorrect proteins are produced cells may not function properly. This is the cause of many _________ diseases.
Inherited diseases
Parents pass on genetic information to their children.
This is means that they pass on genes for many features including ______ ________ and ________.
But sometimes genes are passed on which cause an illness or __________.
Examples of genetic diseases are ___________, sickle cell anaemia and muscular dystrophy.
WORDBANK:
amino acid, bases, double helix, disease, gene, genetic, guanine, haemophilia, hair colour, inherited,
mistakes, peptide, protein, proteins, phosphate, radiation, sequence, triplets, height
Genetics
Organisms pass on some of their genetic information to their offspring
Adult cells have _____ copies of every ______. Sperm and egg cells have ____ copy of every gene.
Each parent will pass on a copy of each gene to their ___________.
The differences between organisms are called __________. There are two types of variation.
__________ where the characteristic can be observed in a distinct grouping like eye colour and fingerprints.
___________ variation is a characteristic that can be measured and shows a range in a group of organisms like
________ and weight.
Some inherited genes will be _________ meaning they will definitely be expressed and some are __________
which means they are not always expressed.
For a recessive gene to be expressed the individual must have _____ of them.
Organisms carry two forms of a gene, these are called ________.
Genetic crosses help work out what the effect of inherited genes will be.
Genetic cross
Genetic information is represented with letters for each _____________.
The capital letter is the________ form of a gene (allele) the lower case is the ________ form of the gene.
The genes an organism has is called its _________ (represented as letters in a cross).
The physical expression of the genes is called the __________ - the appearance of the organism.
WORDBANK:
two, alleles, characteristic, continuous, discrete, dominant, gene, genotype, height, offspring, one,
phenotype, recessive, two, variation, dominant, recessive
An example of a cross might look like this:
In guinea pigs their fur type can either be rough hair or smooth hair. Most Guinea pigs are rough haired.
The hair type is controlled by two alleles. The letter __ will represent the allele for rough hair and the
letter ___ will represent the allele for smooth hair.
Parents (P)
(phenotype)
rough hair
X
(genotype)
___
X
Gametes (sex cells)
__
smooth hair
___
__
First generation (F1)
(genotype)
___
(phenotype)
_____ hair
Then if the F1 are crossed with themselves or self-crossed the following would be produced.
Self-cross
(phenotype)
rough hair
X
rough hair
(genotype)
Rr
X
Rr
Second generation (F2) (to complete this a punnet square is used).
gametes
R
r
R
r
This produces some rough hair and smooth hair Guinea pigs.
Theoretically, __ rough and __ smooth or a ___:___ ratio is produced.
In the real world the actual ratio of characteristics seen in a population will probably not be exactly the
same as the theoretical one. This is because fertilisation is a _________ process.
WORDBANK: 3:1, random, rough, r, 1, r, RR, rr, R, Rr, RR, Rr, rr, Rr, 3, R