Biology Term 1 Flashcards
1
Q
What is the cell cycle?
A
A series of events that take place in a cell involving cell growth, DNA replication and cell division.
It is described as the lifecycle of a cell.
2
Q
State the three stages of the cell cycle
A
- Interphase
- Mitosis
- Cytokinesis
3
Q
What is the interphase?
A
The longest stage of the cell cycle that involves cell growth, the syntheses of new organelles and DNA replication.
4
Q
What does DNA replication involve?
A
- Double helix ‘unzips’ exposing two strands.
- DNA bases align next to complementary bases on the DNA strands.
- Complementary base pairs join.
- Tow identical DNA molecules formed.
5
Q
What is a chromosome?
A
A linear DNA molecule tightly coiled around proteins.
6
Q
What happens to chromosomes durning DNA replication?
A
The DNA in the ‘arms’ of each chromosome (chromatid) is relicated.
7
Q
What is mitosis?
A
A form of cell division that produces two diploid ‘daughter’ cells, both genetically identical to the parent cell.
8
Q
Why is mitosis important in organisms?
A
- Asexual reproduction
- Growth
- Repair of damaged cells
- Cell replacement
9
Q
State the four stages of mitosis
A
P - Prophase
M - Metaphase
A - Anaphase
T - Telophase
10
Q
Outline prophase
A
- DNA condenses, chromosomes become visible
- Nuclear membrane disappeared
11
Q
Outline metaphase
A
Chromosomes line up along the cell equator.
12
Q
Outline anaphase
A
- Spindle fibres attach to each chromosome.
- ‘Arms’ of each chromosome pulled to opposite poles.
- Chromatids separated.
13
Q
Outline telophase
A
- Nucleus of the cell divides.
- Nes membrane forms around each set of chromosomes.
14
Q
What does cytokinesis involve?
A
- Division of the cell membrane and cytoplasm.
- Two genetically identical ‘daughter’ cells produced.
15
Q
What is cancer?
A
- Non-communicable diseases.
- Uncontrolled cell division (due to damaged DNA) results in the formation of a primary tumour.
- Tumour cells break off and spread to other tissues forming secondary tumours.
16
Q
What are percentile charts?
A
- A chart used to monitor growth.
- Measurements (e.g. fetal length or head circumference) can be compared to the expected values at a certain age.
17
Q
What does the 95th percentile mean?
A
95% of measurements will be below the value of the 95th percentile.
18
Q
What can doctors determine from the percentile charts?
A
- Slower growth than normal (below the bottom lines).
- Faster growth than normal (above the top line).
- Abnormal growth (irregular growth patterns).
19
Q
Describe growth in animals
A
- Cell division occurs in all body cells. It occurs at a slower rate in adults that in younger animals as growth stops and cell division is only required for replacement and repair.
- Most cells differentiate for early stage and become specialised. Some adult stem cells retain their ability to differentiate.
20
Q
Describe growth in plants
A
- Cell division can only occur in meristematic tissue. The rate of cell division remains the same throughout a plant’s life.
- Meristematic stem cells can differentiate into any cell type for as long as the plant lives.
- Cell elongation occurs in all cells. Cells expand and enlarge enabling growth of the plant.
21
Q
What are stem cells?
A
Cells that are unspecialised and capable of differentiating into a range of different cell types.
22
Q
What is meant by ‘differentiation’?
A
- The process by which stem cells become specialised.
- Some genes switch on or off, determining cell type.
23
Q
Why is cell differentiation important?
A
It enables the formation of specialised tissues with specific functions e.g. muscle tissue.
24
Q
What are embryonic stem cells?
A
Stem cells found in very early embryos that are unspecialised and capable of differentiating into any cell type.
25
What is the function of embryonic stem cells?
Enable the growth and development of tissues in human embryos.
26
What are adult stem cells?
Stem cells that can differentiate into a limited range of cell types e.g. bone marrow stem cells.
27
What is the primary function of adult stem cells?
Replacement of dead cells e.g. replacement of red blood cells which only live for 120 days.
28
Where are stem cells founds in plants?
Meristems
29
Where is meristem tissue found?
In regions of the plant where cells are continuously dividing, e.g. root tips, shoot tips.
30
Where are meristematic stem cells?
Stem cells found in meristems are unspecialised and capable of differentiating into any cell type during the life of a plant.
31
How can stem cells be used in medicine?
- Stem cells collected.
- Stem cells stimulated to differentiate into specific cell types e.g. heart muscle cells.
- Specialised cells transplanted into the patient.
- Used to treat damage or disease e.g. heart disease.
32
Where can embryonic stem cells be collected from?
- Donor stem cells removed from embryos grown in vitro.
- Patient's own stem cells removed from the umbilical blood before birth.
33
What are the benefits of using stem cells in medicine?
- Treat damage or disease e.g. heart disease, type 1 diabetes.
- Treat diseases that would otherwise be untreatable.
- Used in scientific research.
- Growing organs for transplants.
34
What are the risks of stem cells use in mededicine?
- Transplanted stem cells could cause tumours.
- Finding suitable stem cell donors is a difficult task.
- Stem cells may be rejected by the body (immunosuppressants taken).
- Potential side effects.
- Long term risks of using stem cells unknown.
- Stem cells may become contaminated during preparation and when transplanted transmit infections to the patient, making them sicker.
35
What are the ethical issues related to the use of stem cells in medicine
- The embryos that were used to provide stem cells are destroyed which is seen as unethical and a waste of potential human life.
- May lead to the reproductive cloning of humans.
36
What is DNA?
A double-stranded polymer of nucleotides, would to form a double helix.
37
What are the monomers of DNA?
Nucleotides
38
What are DNA nucleotides made up of?
- Common sugar.
- Phosphate group.
- One of the four bases : A, T, C or G
39
State the full names of the four bases found in nucleotides?
- Adenine
- Thymine
- Cytosine
- Guanine
40
Describe how nucleotides interact to form a molecule of DNA?
- Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand.
- Base connected to each sugar.
- Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds.
41
Define Genome
The entire genetic material of an organism
42
What is a chromosome?
A long, coiled molecule of DNA that carries genetic information in the form of genes.
43
Define gene
A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein.
44
Describe the method used to extract DNA from fruit?
1) Place a piece of fruit in a beaker and crush it.
2) Add detergent and salt, mix.
3) Filter the mixture and collect the liquid in a test tube.
4) Pour chilled ethanol into the test tube.
5) DNA precipitates forming a fibrous white solid.
6) Use a glass rod to collect the DNA sample.
45
Why is detergent added to the crushed fruit?
It disrupts the cell membranes, releasing DNA into solution.
46
Why is salt added to the crushed fruit?
Salt encourages the precipitation of DNA.
47
Why is chilled ethanol added rather water?
DNA is insoluble in ethanol, encouraging its precipitation.
48
Explain how a gene codes for a protein.
- A sequence of three bases in a gene forms a triplet.
- Each triplet codes for an amino acid.
- The order of amino acids determines the structure (i.e. how it will fold) and function of protein formed.
49
Why is the 'folding' of amino acids important in proteins such as enzymes?
The folding of amino acids determined the shape of the active site which must be highly specific in the shape of its substrate.
50
What is protein synthesis?
The formation of a protein from a gene.
51
What are the two stages of protein synthesis?
1. Transcription
2. Translation
52
What does transcription involve?
The formation of mRNA from a DNA template.
53
Outline transcription
1. DNA double helix unwinds.
2. RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand.
3. RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand.
4. mRNA formation complete. mRNA detaches and leaves the nucleus.
54
Describe the difference between mRNA and DNA.
- mRNA is singe stranded whereas DNA is double stranded.
- mRNA uses U whereas DNA uses T
55
Why is mRNA used in translation rather than DNA?
DNA is too large to leave the nucleus so cannot reach the ribosome.
56
What does translation involve?
A ribosome joins amino acids in a specific order dictates by mRna to form a protein.
57
Outline translation
1. mRNA attaches to a ribosome.
2. Ribosome reads the mRNA bases in triplets. Each triplet codes for one amino acid which is brought to the ribosome by a tRNA molecule.
3. A polypeptide chain is formed from the sequence of amino acids which join together.
58
How is tRNA molecule adapted to its function?
Each tRNA molecule has an anticodon which is specific to the codon of the amino acid that it carries.
59
What is mutation?
A random change in the base sequence of DNA which in genetic variants.
60
Describe the effect of a gene mutation is coding DNA.
- If a mutation changes the amino acid sequence protein structure and function may change.
- If a mutation does not change amino acid sequence there is no effect on protein structure or function.
61
What is non-coding DNA?
DNA which does not code for a protein but instead controls gene expression.
62
Describe the effect of a gene mutation in non-coding DNA.
- A mutation may affect the ability of RNA polymerase to bind to non-coding DNA.
- This may affect protein production and the resulting phenotype of the organism.
63
Outline how the work of Mendel helped scientists to develop their understanding of genetics.
- Mendel studied the inheritance of different phenotypes of pea plants.
- He established a correlation between parent and offspring phenotypes.
- He noted that inheritance was determined by 'units' passed on to descendants.
- Using gene crosses, he devised the terms 'dominant' and 'recessive'.
64
Why was Mendel's work initially overlooked?
Scientist's didn't understand Mendel's work as there was no knowledge of genes or DNA at the time.
65
What is a chromosome?
A long, coiled molecule of DNA that carries genetic information in the form of genes.
66
Define gene
A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form protein.
67
What are alleles?
Different version of the same gene.
68
Define genotype
An organism's genetic composition describes all alleles.
69
Describe phenotype
An organism's observable characteristics due to interaction of the genotype and environment (which can modify the phenotype).
70
Define homozygous
Having two identical alleles of a gene e.g. FF or ff.
71
Define heterozygous
Having two different alleles of a gene e.g. Ff.
72
What is a dominant allele?
Describe an allele that is always expressed. Represent with a capital letter e.g. F.
73
What is a recessive allele?
An allele that is only expressed in the absence of a dominant allele.
Represented with a small letter e.g. f.
74
What is monohybrid inheritance?
The inheritance of a single gene.
75
What is the problem with single gene crosses?
Most characteristics are controlled by multiple alleles rather than just one.
76
What are sex chromosmes?
A pair of chromosomes that determine six:
- Males have an X and a Y chromosome.
- Females have two X chromosomes.
77
Why does the inheritance of a Y chromosome mean that an embryo develops into a male?
Testes development in an embryo is stimulated by a gene pre
78
Other than using a Punnett square, how else can monohybrid inheritance be represented.
Using a family pedigree
79
What is a sex-linked characterisitc?
A characteristic that is coded for by an allele found on a sex chromosome.
80
Why are the majority of genes found on the X chromosome rather than the Y chromosome?
The X chromosome is bigger than the Y chromosome so more genes are carried on it.
81
Why are men more likely to show the phenotype for a recessive sex-linked trait than women?
- Many genes are found on the X chromosome that have no counterpart on the Y chromosome.
- Women (XX) have two alleles for each sex linked gene whereas men (XY) often have one alleles ,', only one recessive allele is required to produce the recessive phenotype in males.
82
Give an example of a characteristic that is determined by more than one allele.
Blood group is determined by three alleles: I^A, I^B, I^O.
83
Name the four different blood groups.
A, B, AB, O
84
What are codominant alleles?
Alleles that equally contribute to an organism's phenotype. They are expresses to an equal extent.
85
Describe codominance in blood groups?
- I^A and I^B are codominant.
- I^A I^B gives the blood group AB
86
Why does I^A I^0 give blood group A?
- I^0 is recessive to I^A.
- - I^A is dominant and is expressed giving blood group A.
87
What are the possible genotypes for blood group B?
- I^B I^O
- I^B I^B
88
What is the genotype of blood group 0?
I^O I^O
89
State the two types of cell.
Eukaryotic (animals and plants) and prokaryotic.
89
What is the difference between a eukaryotic and prokaryotic cell?
A eukaryotic cell contains a nucleus and membrane-bound organelles. A prokaryotic cell does not.
90
List the components of both plan and animal cells
- Nucleus
- Cytoplasm
- Cell membrane
- Mitochondria
- Ribosomes
90
How is genetic information stored in a eukaryotic cell?
Withing the nucleus, arranged in chromosomes.
91
Other than storing genetic information, what is the function of the nucleus?
Controls cellular activities.
92
Describe the structure of the cytoplasm.
- Fluid component of the cell.
- Contains organelles, enzymes and dissolved ions and nutrients.
93
What is the function of the cytoplasm?
Site of cellular reactions, e.g. first stage of respiration.
94
What is the function of the cell membrane?
Controls the entry and exit of materials into and out of the cell.
95
What is the function of the mitochondria?
Site of later stages of aerobic respiration in which ATP is produced.
96
What is the function of ribosomes?
Joins amino acids in a specific order during translation.
97
Which organelles are found in plant cells only?
- Large, permanent vacuole
- Cell wall
- Chloroplast
98
What is the cell wall made of?
Cellulose
99
What is the function of the cell wall?
- Provide strength
- Prevents the cell bursting when water enters by osmosis.
100
What does the permanent vacuole contain?
A solution of salts, sugars and organic acids.
101
What is the function of the permanent vacuole?
Support the cell, maintaining its turgidity.
102
What is the function of the choroplasts?
Site of photosynthesis
103
When looking at a cell using a light microscope, why do chromoplast appear green?
Contains chlorophyll, a green pigment.
104
List the organelles found in prokaryotic cells?
- Chromosomal DNA
- Plasmid DNA
- Cell wall
- Cell membrane
- Ribosomes
- Flagella
105
How is genetic information stored in a prokaryotic cell?
Found free within the cytoplasm as:
- Chromosomal DNA (single large loop of circular DNA)
- Plasmid DNA
106
What are plasmids?
- Small, circular loops of DNA found free in the cytoplasm and sperate form the main DNA.
- Carry genes that provide genetic advantages e.g. antibiotic resistance.
107
What is the prokaryotic cell wall composed of?
Peptidoglycan
108
What is a flagellum?
- Long, rotating, 'whip-like' protrusion.
- Enables bacteria to move.
109
What is a haploid cell?
A cell that contains a single copy of each chromosome (half the number of chromosomes)
e.g. 23 chromosomes in humans.
110
What is a diploid cell?
A cell that contains two copies of each chromosome (full set of chromosome)
e.g. 46 chromosomes in humans.
111
What are gamets?
- Reproductive cells (e.g. egg and sperm cells)
- They are haploid cells.
112
Describe sexual reproduction in terms of chromosome number.
- Two haploid gametes fuse.
- Resulting embryo has two chromones for each gene and two copies of each ,', diploid.
113
Describe how egg cells are adapted to their function.
- Haploid nucleus contains genetic material.
- Mitochondria in cytoplasm produce energy for the developing embryo.
- Cytoplasm contains nutrients for the developing embryo
- Cell membrane hardens after fertilisation, preventing the entry of other sperm and ensuring the zygote is diploid.
114
Describe how sperm cells are adapted to their functions.
- Haploid nucleus contain genetic information.
- Tail enables movement.
- Mitochondria provide energy for tail movement.
- Acrosome contains enzymes that digest the egg cell membrane.
115
Where are ciliated epithelial cells found?
Found lining the surface of structures such as the respiratory tract and uterus.
116
Describe the function of ciliated epithelial cells lining the airways.
Move in synchronised waves to beat mucus (containing dirt and pathogens) up to the back of the throat where it can be swallowed.
117
What is magnification?
The number of times bigger an image appears compared to the size of the specimen.
118
How can the total magnification of an image be calculated from lens powers?
Total magnification = eyepiece lens magnification X objective lens magnification
119
How can the magnification of an image be calculated?
Magnification = Size of image
______________________
Size of specimen
120
What is resolution?
The smallest distance between two objects than can be distinguished.
121
How does a light microscope work?
Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed.
122
What are the advantage of light microscopes?
- Inexpensive
- Easy to use
- Portable
- Observe both dead and living specimens
123
What is the disadvantage f light microscopes?
Limited resolution
124
How does an electron microscope work?
It uses a beam of electrons which are focused using magnets. The electrons hit a fluorescent screen which emits visible light, producing an image.
125
Name the two types of electrons microscope.
- Transmission electron microscope (TEM)
- Scanning electron microscope (SEM)
126
What is the advantage of electron microscopes?
Greater magnification and resolution.
127
Why do electron microscopes have a greater magnification and resolution?
They use a beam of electrons which has a shorter wavelength than photons of light.
128
How have electrons microscopes enabled scientists to develop their understanding of cells?
- Allow small sub-cellular structures (e.g. mitochondria, ribosomes) to be observed in detail.
- Enable scientist to develop more accurate explanations about cell structure relates to function.
129
What are the disadvantage of electron microscopes?
- Expensive
- Large so less portable
- Require training to use
- Only dead specimens can be observed
130
How do you convert from m to mm?
x 1000 (x10^3)
131
How do you convert from m to μm?
x 1 000 000 (x 10^6)
132
How do you convert from m to nm?
x 1 000 000 000 (x 10^9)
133
How do you convert from nm to m?
÷ 1 000 000 000 (10^-9)
134
How do you convert from m to pm?
x 1 000 000 000 000 (x10^12)
135
What are the two causes of variation withing a species?
- Genetics
- Environment
136
What is genetic variation?
- Variation in the genotype of organisms of the same species due to the presence of different alleles.
- Creates differences of phenotypes.
137
What creates genetic variation in a species?
- Spontaneous mutation
- Sexual reproduction
138
What is a mutation?
A random change to the base sequence in DNA which results in genetic variants.
139
State the three types of gene mutation.
- Insertion
- Deletion
- Substitution
140
How may a gene mutation affect an organism's phenotype?
- Neutral mutation does not change the sequence of amino acids. Protein structure and function same. No effect on phenotype.
- Mutation may cause minor change in an organism's phenotype e.g. change in eye colour.
- Mutation may completely change the sequence of amino acids. This may result in a non-functional protein. Several changes to phenotype.
141
What is environmental variation?
- Variation in phenotype that are acquired during the lifespan of an organism.
- Due to environmental factors e.g. diet, lifestyle, climate, exposure to light ect.
142
What is the Human Genome Project?
- Scientific research project involving thousands of scientists across the globe which successfully mapped the entire human gnome.
- Scientists now aim to identify the function of every gene in the human genome.
143
How can the results of the Human Genome Project be applied to medicine?
- Enables scientist to understand how lifestyle factors interact with genes - identifying predisposing to disease and possible preventions.
- Disease-causing alleles identified more rapidly and the appropriate treatment prescribed earlier on.
- Scientist can predict an individual's response to certain drugs. New drugs can be developed which are tailored to a specific allele.
144
What are the drawbacks associated with the discoveries of the Human Genome Project?
- Knowledge of predisposition to a disease can be stressful.
- Social pressure influencing the decision to have children.
- Discrimination by employers, insurance first ect.
