B3- Living and Growing Flashcards
What is mitochondria?
Structures in a cell where respiration takes place
What does the number of mitochondria in the cytoplasm depend on?
The activity of the cell
Which cells have large numbers of mitochondria?
Liver or muscle cells because the liver carries out many functions and muscle cells need to contract
What are ribosomes?
Structures in a cell where protein synthesis takes place
What does the nucleus contain?
Genes
What is a gene?
Section of DNA that codes for a particular characteristic
What is the structure of DNA?
- two strands coiled to form a double helix
- each strand contains chemicals called bases
- bases cross links between strands
- each gene contains a different sequence of bases
Where are proteins made?
Cytoplasm
How does DNA leave the nucleus?
DNA itself cannot leave the nucleus, so a copy of that gene needs to be made so it can leave the nucleus and carry the code to the cytoplasm
What are the 4 bases?
A, T, C, G
What is complementary base pairing?
The bases always pair the same way
A-T and G-C
What does the DNA base code control?
Which protein is made
How is an amino acid coded for?
By a sequence of three bases
What does the mRNA do?
messenger RNA carries the code needed to produce a protein from the DNA to the ribosomes
What did Watson and Crick do?
- built a model of DNA using data from other scientists
- photographs were taken using x-rays showing that DNA had two chains wound in a helix
- data indicates that the bases occurred in pairs
When did Watson and Crick work out the structure of DNA?
1953
When did Watson and Crick win the Nobel Prize?
1962
Why was there a delay between Watson and Crick receiving the prize?
Other scietists needed to check the discovery was correct before giving them the prize
What are all proteins made of?
Long chians of amino acids joined together
What are the 4 types of protein functions?
- structural proteins used to build cells and tissues (e.g. collagen)
- hormones which carry messages to control a reaction (e.g. insulin)
- carrier proteins (e.g. haemoglobin)
- enzymes
Each protein has its own number and order of amino acids.
What does this mean?
Each protein molecule is a different shape and gives it a different function
Why are enzymes biological catalysts?
They speed up reactions in the body
What chemical reactions do enzymes catalyse?
- respiration
- photosynthesis
- protein synthesis
What is the ‘lock and key mechanism’?
- substrate molecule fits into active site of enzyme
- forming an enzyme-substrate complex
- releasing its products
What is specificity in enymes?
Each enzyme can only work on a particular substrate
What is the optimum?
Enzymes work best at a particular temperature and pH. Any change away from the optimum will slow down the reaction
How is enzyme activity affected by pH and temperature?
- low temperatures, molecules are moving slowly so enzyme and substrate are less likely to collide
- at very high or low pH values and high temperatures, enzyme active site changes shape (denatures) so substrate cannot fit and cannot react quickly
How do you work out the rate of reaction?
By calculating temperature coefficient, called Q10 for a 10ºC change in temperature
Q10= rate at higher temperature / rate at lower temperature
What are mutations?
DNA within cells have been altered
How might mutations occur?
Spontaneously but can be made to occur more often by radiation or chemicals
What can mutations cause?
- production of different proteins
- harmful, but may not have an effect
- occasionally they might give the individual and advantage
What allows different cells to perform different functions?
Different genes are switched off in different cells
What do gene mutations do?
Alter or prevent the production of protein that is normally made because they change the base code of DNA, so change order of amino acids in the protein
Why is respiration important?
It releases energy from food and this energy is trapped in ATP, which can be used to provide energy for many different processes in living organisms
What is the aerobic respiration equation?
C6H12O6 + 6O2 → 6H2O + 6CO2
When does the body respire anaerobically?
Often during exercise, when the muscles do not receive sufficient oxygen
What is the word equation for anaerobic respiration?
glucose → lactic acid (+energy)
What are the disadvantages of anaerobic respiration?
- lactic acid that is made builds up in muscles, causing pain and fatigue
- anaerobic respiration releases much less energy per glucose molecule that aerobic respiration
What is oxygen debt?
The incomplete breakdown of glucose resulting in the build up of lactic acid
Why does breathing rate and heart rate stay high during recovery?
- rapid blood flow can carry lactic acid away to the liver
- extra oxygen can be supplied, enabling the liver to break down the lactic acid
What experiments can be used to measure the rate of respiration?
- measuring how much oxygen is used up - the faster it is consumed, the faster the respiration rate
- the rate at which carbon dioxide is made
How can you calculate respiratory quotient?
RQ = carbon dioxide produced / oxygen used
What is the metabolic rate?
The sum of all the reactions that are occurring in the body. If metabolic rate is high, more oxygen is needed, as aerobic respiration is faster
What can affect respiration rate?
Changes in temperature and pH because they affect enzymes, and respiration is controlled by enzymes
What does multicellular mean?
Organisms made up of many specialised cells
What are the advantages of being multicellular?
- organism can become larger and more complex
- different cells to take on different jobs
Cell differentiation
What systems must a multicellular organism have?
- allow communication between all cells in the body
- supply all cells with enough nutrients
- control exchanges with environment such as heat and gases
What process produces new cells for growth?
Mitosis
What are the products of mitosis?
Genetically identical cells
What must happen before mitosis occurs?
DNA replication
Why must DNA replication occur before cell division?
So that each cell produces still has two copies of each chromosome
What are diploid cells?
Cells that have two copies of each chromosome
What is the process of mitosis?
- cell resting
- each chromosome is copied, single strand forms double-stranded ‘X’ shape
- spindle forms, chromosomes arranged along equator
- chromosome single strands move to poles of cell
- two genetically identical cells are produced
What is the process of DNA replication?
- two strands of DNA molecule ‘unzipping’ to form single strands
- new double strands forming by DNA bases lining up in complementary base pairings
What process produces gametes?
Meiosis
What are haploid cells?
Cells that contain only one chromosome from each pair
What produces genetic variation?
The zygote gets one copy of a gene from one parent and another copy from the other parent
How is the sperm structure adapted to its function?
- many mitochondria to provide energy for swimming to the egg
- an acrosome that releases enzymes to digest the egg membrane
What is the process of meiosis?
diploid cells- the single strands are copied to make X shaped chromosomes
- chromosomes pair up
- one from each pair moves to each pole
- strands of each chromosome are pulled apart to opposite poles
- four new haploid cells form, all genetically different from each other
What is the liquid part of the blood called?
Plasma
What does plasma carry around the body?
- dissolved substances from tissue to lungs
- carbon dioxide
- hormones from glands to their target cells
- plasma proteins such as antibodies
- waste substances such as urea
How are red blood cells adapted to their function?
- very small so they can pass through blood vessels
- shaped like biconcave discs (large surface area to exchange oxygen quicker)
- contain haemoglobin to combine with oxygen (makes them appear red)
- don’t have a nucleus so more haemoglobin can fit
What is formed when haemoglobin reacts with oxygen?
Oxyhaemoglobin
What happens when oxyhaemoglobin reaches the tissues?
Oxygen is released
(the reaction is reversible)
What does the biconcave shape of red blood cells provide?
Larger surface area to volume ratio to exchange oxygen more quickly
What are the different types of blood vessels?
- arteries
- veins
- capillaries
What jobs do the blood vessels have?
- arteries transport blood away from the heart to the tissues
- veins transport blood back to the heart from tissues
- capillaries link arteries to veins and allow materials to pass between blood and tissues
How are arteries adapted?
Thick muscular and elastic wall to resist high pressure
How are veins adapted?
Have large lumen and valves to try keep blood moving back to the heart because the pressure is low
How are capillaries adapted?
Permeable walls so substances can be transferred between blood and tissues
How does the heart circulate blood?
- atria receive blood from veins
- ventricles pump blood out into arteries
- valves prevent backflow of blood
- pulmonary vein and vena cava are the main veins carrying blood back to heart
- aorta and pulmonary artery carry blood away from heart
Why does the left ventricle have a thicker muscle wall?
It has to pump blood all around the body rather than just to the lungs
What is a double circulatory system?
Where blood is pumped to the lungs then returned to the heart before being pumped round the body
What are the advantages of a double circulatory system?
Blood is at a higher pressure so flows to the tissues at a faster rate
How are bacterial cells different from plant and animal cells?
They lack a ‘true’ nucleus, mitochondria and chloroplasts
Where is DNA found in a bacterial cell?
In the cytoplasm as a single circular strand or chromosome
What does the growth curve diagram show?
There are two phases which involve rapid growth: one after birth and in adolescence
What is the best measure of growth?
Dry mass
What is good and bad about measuring growth by length?
Easy to do but measures growth in one direction only
Why is measuring wet mass hard?
Difficult for some organisms such as trees, but easier for animals. However, water content of organisms can vary with time
What is good and bad about measuring dry mass?
It involves killing the organism and driving off water, but it does measure the true growth of the whole organism
Why does different parts of the organism grow at different rates?
Different parts of the organism may be needed at different times during the life of the organism
What are stem cells?
Unspecialised body cells (found in bone marrow) that can develop into other, specialised cells that the body needs e.g. blood cells
Where can you obtain stem cells?
From embryos
What can stem cells be used for?
Treating some medical conditions
What are the issues with stem cell research?
It is wrong because embryos are destroyed
It is acceptable as it can treat life-threatening diseases
Why are adult stem cells not used?
They are unspecialised cells that can develop into many (but not all) types of cells and are not very easy to find
What are the differences between plant and animal growth?
- animals tend to grow to a certain size, but plants can carry on growing
- plant cell division only happens in meristems (tips of roots and shoots)
- main way plants gain height is by cells enlarging rather than dividing
- plants keep ability to differentiate, but most animal cells lose it at an early stage
What are problems with selective breeding?
- may lead to interbreeding (two closely related individuals mate)
- health problems within species
What can interbreeding lead to?
Reduce the variety of alleles in the population (gene pool), which can lead to:
- increased risk of harmful recessive characteristics showing up in offspring
- reduction in variation, so that populations cannot adapt to change so easily
What are the risks and advantages of genetic engineering?
Advantage
- organisms with desired features can be produced quickly
Risk
- inserted genes may have unexpected harmful side effects
What are examples of organisms made using genetic engineering?
- rice containing beta-carotene to increase the amount of vitamin A
- genetically engineered bacteria to produce human insulin
- crop plants made resistant to herbicides, frost, or diseases
What are the ethical issues with genetic engineering?
- worry about the possible long term effects (damage to natural ecosystems)
- it is morally wrong, whatever the intended benefits
What steps are taken for genetic engineering?
- desired characteristics are selected
- genes responsible are identified and removed (isolation)
- genes inserted into other organisms
- organisms allowed to reproduce (replication)
What is gene therapy?
Process of using genetic engineering to change a person’s genes and cure certain disorders
Why is changing genes in gametes controversial?
It is difficult to decide which parents should be allowed to change as it could lead to ‘designer babies’
How does cloning using nuclear transfer work?
Involves removing the nucleus from a body cell and placing it into an egg cell that has had its nucleus removed
Why would animals be cloned?
- mass-produce animals with desirable characteristics
- produce animals that have been genetically engineered to provide human products
- produce human embryos for stem cell therapy
What are the dilemmas with human cloning?
People see it as wrong to clone people as they will not be ‘true individuals’
What steps where involved when Dolly the sheep was cloned?
- donor egg had its nucleus removed
- egg cell nucleus replaced with nucleus from udder cell (body cell)
- egg cell given an electric shock to divide
- embryo implanted into a surrogate mother sheep
- embryo grew into a clone of sheep from which the udder cell came
What are the advantages and disadvantages of plant cloning?
Advantage
- growers can be sure of characteristics of each plant
- mass-produce plants that may be difficult to grow from seed
Disadvantage
- if plants become susceptible to disease/change in environment, then all plants are affected
- lack of genetic variation in plants
What are the steps of tissue culture cloning?
- plant is selected that has certain characteristics
- large number of small pieces of tissue are cut from plant
- small pieces of tissue are grown in test tubes or dishes containing a growth medium
- aseptic technique is used at all stages to stop any microbes infecting plants
Why are plant cells easier to clone?
Plant cells retain the ability to differentiate, but animal cells lose this ability at an early stage
