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Science B2 Topic 1
Edexcel GCSE additional science biology: the building blocks of cells
| Question | Answer |
|---|---|
| What are cells? | Cells are the basic unit of life in which chemical reactions needed to sustain life take place |
| What do animal cells contain and what are the functions of these features? | Cell membrane: controls the movement of substances in and out of the cell. Cytoplasm: contains organelles and is where many chemical reactions take place. Nucleus: contains DNA + controls cell activity. Mitochondria: organelles where respiration occurs |
| What do plant cells contain that animal cells don't? | Large vacuole: large space filled with cell sap which keep cells rigid. Cell wall: made of cellulose so makes cell keep its shape. Chloroplasts: organelles that contain chlorophyll which absorbs light energy for photosynthesis |
| What do bacteria cells contain and what are the functions of these features? | Chromosomal DNA is large loops containing most genetic info. Plasmid DNA is small loops containing extra info. Cell wall supports cell (not made of cellulose). Flagella helps to move (not always present). Cell membrane controls what enters and exits cell. |
| How do light microscopes magnify images? | By passing light through a specimen and magnifying lenses: objective lens and eyepiece lens |
| How do you calculate the total magnification of light microscopes? | Multiply the magnification of the two lenses together |
| How do electron microscopes magnify images? | They use a beam of electrons to produce an image |
| What are the advantages and disadvantages of a light microscope? | Advantages: cheaper to use and operate, doesn't require a vacuum, natural colour of specimen is maintained, smaller and portable Disadvantages: magnification only up to x2000, image is less clear and detailed |
| What are the advantages and disadvantages of an electron microscope? | Advantages: magnification up to x500,000, image is very detailed and clear Disadvantages: very expensive to buy and operate, requires a vacuum, image is in black and white, very large, requires special room |
| What are chromosomes? | Chromosomes are structures made up of DNA found in the nucleus |
| What is a gene? | A section of DNA that codes for a specific protein, which causes the development of a particular feature |
| What structure/shape is DNA? | DNA is a polynucleotide, as it is made up of two strands of nucleotides in a double helix shape |
| How are the strands of nucleotides in DNA joined? | By a series of complementary base pair joined at regular intervals by weak hydrogen bonds. Adenine and thymine join together, cytosine and guanine join together |
| How was DNA discovered? | Wilkins and Franklin directed beams of X-rays at purified DNA to see the way the x-rays were scattered as this showed how groups of atoms are arranged. Crick and Watson used these images to build a 3D molecular model of DNA |
| What was the Human Genome Project? | An international effort to work out the sequence of the 3 billion base pairs that make up the human genome |
| What is a genome? | All the genes in an organism listed in order of every base |
| What are the advantages of knowing the human genome? | •development of personalised medicines •improved testing for genetic disorders •developemtn |
| What is genetic engineering? | The process where a gene from one organism is transferred to the DNA of another organism |
| What are some examples of genetically modified organisms? | * insulin-producing bacteria: gene for human insulin in plasmid * golden rice plants: beta carotene in rice plant * herbicide-resistant crop plants: crops are resistant to herbicides |
| What are the advantages and disadvantages of the GMO: insulin-producing bacteria? | Adv: vegans, cheap, large quantities, supply of insulin unaffected by animal diseases Disadv: doesn't suit everyone |
| What are the advantages and disadvantages of the GMO: golden rice plants? | Adv: beta-carotene is used in humans to produce vitamin A so this will reduce vitamin A deficiency Disadv: GM crops are expensive, may not contain enough beta-carotene to make a difference, could be harmful, could crossbreed |
| What are the advantages and disadvantages of the GMO: herbicide-resistant crop plants? | Adv: farmers can use herbicides without killing desirable plants, this allows crops to grow better (more space, more nutrients) Disadv: could crossbreed to form herbicide-resistant weeds, loss of biodiversity, loss of shelter / food for animals |
| What is a diploid cell? | A cell that contains two copies of each chromosome (all human body cells are diploid except gametes) |
| What is mitosis? | Mitosis is the process by which a diploid cell divides to form two daughter cells that are also diploid and are genetically identical to each other and the parent cell |
| How does mitosis take place? | 1. chromosomes are copied in DNA replication 2. chromosomes separate 3. cell divides, producing two daughter cells |
| When does mitosis occur? | During growth, repair of damaged cells, and asexual reproduction |
| What is asexual reproduction? | Asexual reproduction is the formation of a new individual without fertilisation using mitosis to create offspring identical to the parent organism. Bacteria split in half. Plants grow plantlets which split off to grow on their own. |
| What is a haploid cell? | A cell that contains only one copy of each chromosome e.g. gametes |
| What is meiosis? | Meiosis is the process by which a diploid cell divides to form four daughter cells that are haploid and are all genetically different from each other |
| How to meiosis take place? | 1. chromosomes are copied in DNA replication 2. chromosomes separate 3. cell divides once to separate 2 sets of chromosomes 4. cell divides again to separate the copies of the chromosomes, producing 4 haploid cells |
| What is sexual reproduction? | Sexual reproduction is when two gametes fuse to produce a diploid zygote cell, which develops later on into an embryo |
| What is cloning? | Cloning is the process by which a genetically identical copy of an organism is created |
| How do you clone a mammal? | A diploid nucleus is taken from a cell form the animal that is to be clones and is put in an egg cell that has been enucleated. The cell is given an electric pulse to start mitotic division and is placed in the uterus of the surrogate mammal |
| How do you clone a plant? | Take cuttings of the plant - this grow by cell division into new clone plants |
| What are some advantages of cloning mammals? | * mammals with a desired characteristic will pass on their advantage. * genetically modified mammals will pass on their engineered genes. * clones organs could be made for transplants so that the body doesn't destroy the cells of a transplant |
| What are some disadvantages of cloning mammals? | * clones aren't always healthy. * very few embryos develop successfully. *expensive |
| What are stem cells? | Stem cells are unspecialised cells that can differentiate into more cells or different types of specialised cells |
| What is the difference between embryonic and adult stem cells? | Embryonic stem cells are cells from an early age of division of an embryo, and they can differentiate into almost any type of specialised cell. Adult stem cells can only differentiate into a few types of specialised cell. |
| What are advantages and disadvantages of embryonic stem cell research? | Adv: easy to extract, can differentiate into almost any kind of specialised cell, could be taken from a clone of the patient to avoid rejection. Disadv: ethical issues (embryo dies), could be used illegally to clone humans |
| What are advantages and disadvantages of adult stem cell research? | Adv: no ethical issues, can be taken from the patient to avoid rejection. Disadv: can only differentiate into a few types of specialised cell, difficult to find and extract |
| What can stem cells be used for? How many times can they differentiate? | They can replace faulty cells with healthy ones. However they can only differentiate into a specialised cell once. |
| What is protein synthesis? | The manufacture of proteins by synthesising chains of amino acids |
| What is the genetic code? | The order of bases on a DNA strand, which determines the order of the amino acids in teh protein |
| What are the two stages of protein synthesis (include the order)? | 1) transcription 2) translation |
| Describe transcription | Takes place in the nucleus. The weak hydrogen bonds are broken so the DNA separates into two strands.One strand of DNA is used as a template, and the complementary bases to this strand link up, forming mRNA.mRNA moves into the cytoplasm |
| Describe translation | The mRNA attaches to a ribosome which decodes the bases in base triplets (codons). For every codon, the tRNA with the complementary base pairs matches up. The tRNA releases the amino acid it is carrying onto the polypeptide, which folds to form a |
| What is the difference between DNA and RNA? | RNA has a single strand rather than two, and has a base called uracil instead of thymine. |
| How are proteins adapted to their purpose? | Keratin forms strong, fibrous tissues - found in hair and nails which are strong and hard. Haemoglobin and insulin have globular shapes allowing them to move around inside cells and the body easily. |
| What is a mutation? | A mutation is the change in the sequence of bases in the genetic code |
| Why do some mutations have an effect on the protein but others don't? | Some mutations have no effect on the amino acid sequence so don't affect the protein. Others cause one amino acid to be replaced by another, so the polypeptide twists incorrectly and doens't function properly. |
| What is an example of a harmful mutation? | A mutation in the normal allele for the haemoglobin gene causes it to become a sickle-cell allele, which produces sickle red blood cells, which stick together in long fibres and get stuck in small blood vessels |
| What is an example of a beneficial mutation? | A mutation in bacteria can make them resistant to antibiotics |
| What is an enzyme? | A protein and a biological catalyst, so it speeds up the rate of a reaction without being changed by the reaction |
| When are enzymes used inside cells? | DNA replication, protein synthesis |
| When are enzymes used outside cells? | Digestion in the mouth, stomach and small intestine |
| What do enzymes work on? | Enzymes work on a substrate that fits in the active site of the enzyme |
| What is the 'lock and key' hypothesis? | An idea that each substrate will only fit into one shape of active site - each key will only fit into one lock |
| Enzymes are highly ... ? | specific for their substrate |
| What do carbohydrases and proteases catalyse? | Carbohydrases catalyse the breakdown of carbohydrates. Proteases catalyse the breakdown of proteins. |
| What is the rate of a reaction catalysed by an enzyme is dependent on? | * temperature (too low = slow, too high = denatured) * pH (too low or too high = denatured) * substrate concentration (both increase until enzyme can't work any faster) |
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