Biology gcse

• What are the parts of an animal (and plant) cell?

  Nucleus

  Cytoplasm

  Cell membrane

  Mitochondria

  
• What are parts of a plant cell?

  Rigid cell wall

  Large vacuole

  Chloroplasts

  (nucleus, cytoplasm, cell membrane and mitochondria)
• What does the nucleus do?

  Contains DNA that controls what the cell does
• What does the cytoplasm do?

  Its a gel-like substance where most of the chemical reactions happpen
• What does the cell membrane do?

  Holds the cell together and controls what goes in and out
• What does the mitochondria do?


  This is where most of the reactions for respiration take place. Respiration releases energy that the cell needs to work.
• What does the rigid cell wall do?

  It is made up of cellulose and it gives support for the cell
• What does the large vacuole do?

  Contains cell sap, a weak solution of sugar and salts
• What do chloroplasts do?

  This is where photosynthesis occurs. They contain a green substance called chlorophyll.
• What are the features of a bacteria cell?

  Chromosomal DNA

  Plasmids

  Flagellum

  Cell wall
• What is chromosomal DNA?

  Chromosomal DNA controls the cells activities and replication. It floats free in the cytoplasm.
• What are plasmids?


  Plasmids are small loops of extra DNA that aren't part of the chromosome. Plasmids contain genes for things like drug resistance and can be passed between bacteria.
• What is the flagellum?


  The flagellum is a long, hair-like structure that rotates to make the bacterium move.
• What does the cell wall do?

  Support the cell
• What is magnification?


  How much bigger the image is that the specimen
• How do you work out magnification?


  length of image / length of specimen
• What is the difference between light microscopes and electron microscopes?

  Light microscopes let us see things like the nuclei, chloroplasts and mitochondria. Electron microscopes let us see much smaller things in more detail like the internal structure of mitochondria and chloroplasts and even tinier things like plasmids.
• What is DNA?


  DNA is the complex chemical that carries genetic information. DNA is found in chromosomes which are found in the nucleus of most cells.
• What is the structure of DNA? (6marker)

  -A DNA molecule has two strands coiled together in the shape of a double helix.

  -The two strands are hold together by chemicals called bases. The four bases are adenine, thymine, guanine and cytosine.

  -The bases are paired, and they always pair up in the same way; A-T and C-G. This is called base pairing.

  -The base pairs are joined together by weak hydrogen bonds.
• What is a gene?


  A gene is a short piece of DNA that codes for a specific protein. You have genes for hair structure, eye colour enzymes and every other protein in your body.
• Who discovered the structure of DNA?

  -Rosalind Franklin and Maurice Wilkins worked out DNA had a helical structure by directing beams of X-rays onto crystallised DNA and looking at the patterns of x-rays formed as they bounced off.

  -James Watson and Francis Crick used these ideas along with the idea the amount of adenine+guanine matched the amount of thymine+cytosine to make a model of the DNA molecule where all the pieces fitted together.
• What would be a practical to extract DNA?(6 marker)

  -Mash or chop fruit or vegetable (e.g kiwi) and mix with salty water and detergent to break open the cells and help release the DNA from the nuclei.

  -Add protease enzyme to the filtered mixture to break up proteins in cell membranes and so release more DNA.

  -Add ice cold ethanol carefully down inside the tube into the mixture. The ethanol makes the DNA separate from the liquid so it is easy to lift out.
• How does a cell make proteins?

  By stringing amino acids together in a particular order. There's only 20 different amino acids that are used to make up thousands of different proteins. The order of bases in a gene tells cells in what order to put the amino acids together. Each set of three bases (triplet) codes for a particular amino acid.
• What can DNA determine?

  Which genes are switched on or off and so which proteins the cell produces e.g keratin. That in turn determines what type of cell it is e.g. red blood cell, skin cell.
• What are proteins made by?

  Proteins are made in the cell by oraganelles called ribosomes.
• Why does the cell need mRNA?

  Because DNA is found in the nucleus and can't move out of it because its too big. The cell needs to get the information from the DNA to the ribosome in the cell cytoplasm. This is done by using a molecule called mRNA, which is very similar to DNA, but it's shorter and only a single strand. Also, instead of thymine, mRNA has the base uracil (u), which pairs with adenine. mRNA is like a messanger between the DNA in the nucleus and the ribosome. It happens during transcription and translation.
• What happens during transcription?

  -Transcription takes place in the nucleus.

  -The weak hydrogen bonds break and a section of DNA is unwound and the two strands separate.

  -One strand is used as a template.

  -Complementary bases to this strand link to it.

  -mRNA is formed.

  -mRNA stands for messenger RNA

  -mRNA moves out of the nucleus into the cells cytoplasm
• What happens during translation?


  -Translation takes place in the cytoplasm when the mRNA attaches to a ribosome.

  -The ribosome moves along the mRNA in one direction reading a triplet of bases (codon) at a time.

  -tRNA molecules bring amino acids to thee ribosome. The amino acids attached to each tRNA molecule depends on the order of bases in the tRNA.

  -Complementary bases of tRNA pair with the bases of the mRNA strand.

  -Amino acids that are close together are joined to make an amino acid chain (a polypeptide)

  -Every protein is formed from a specific number of amino acids in a particular order. The order of the bases in the DNA defines the order in which the amino acids are joined together. So one section of DNA codes for one particular protein.
• What do mutations do?


  A mutation is a change in an organisms DNA base sequence. This may change the amino acid that is added to the chain during translation on the ribosome.
• What could a harmful mutation change do?

  A harmful mutation could cause a genetic disorder, for example, cystic fibrosis
• What can a beneficial mutation do?

  A beneficial mutation could produce a new characteristic that is beneficial to an organism e.g. a mutation in genes on bacterial plasmids can make them resistant to antibiotics
• What can neutral mutations do?

  Some mutations are neither harmful nor beneficial e.g. they don't affect a proteins function
• What does the haemoglobin (in blood) do?

  Carries oxygen to red blood cells. They have a globular shape
• What do hormones do?

  Hormones are transported in blood to target cells. They have a globular shape
• What does the collagen do?

  The collagen is in tendons and ligaments. Ligaments hold bones together and tendons attach muscles to bones.
• Why does the shape of a protein matter?

  The shape of a protein affects the way it works. The sequence of amino acids gives each protein a particular 3D shape. These shapes may be globular (blobbly) or fibrous (long,strong fibres)
• Enzymes have a very specific shape that allows them to work effectively. Why might a gene with a mutation change the activity of an enzyme? Refer to active site in your answer


  A gene mutation can change the base sequence in DNA. If this change produces a different amino acid sequence, this may change the shape of the active site. The shape of the active site controls how well an enzyme works. If the shape of the active site matches the shape of the substrate better, then the enzyme will work better. But if the shape of the active site is not as good a match, then the enzyme will not work so well.See an expert-written answer!We have an expert-written solution to this problem!
• What are enzymes?


  Enzymes are biological catalysts that control reactions in the body.
• What is a catalyst?


  A catalyst is a substrate which increases the speed of a reaction without being changed or used up in the reaction.
• What is meant by the 'lock and key' hypothesis for enzymes?

  Each enzyme has an active site. Some substrates may or may not fit the active site. If the substrate matches the shape of the active site, the substrate molecules hold them close together so bonds can form between them and make a product. If the product molecule doesn't fit the active site, it is released from the enzyme. Enzymes usually only join with one substrate as they have a high specificity for their substrates.