biology paper 1 edexcel

• animal cell

  nucleus- contains DNA

  mitochondria- responsible for aerobic respiration

  cell membrane-controls what enters and leaves the cell

  ribosomes-protein synthesis

  cytoplasm- chemical reactions
• cell membrane is made up of phospholipids, proteins and carbohydrates
• plant cells have chloroplasts which contain the pigment chlorophyll that absorbs light energy to make glucose from carbon dioxide and water through photosynthesis.
• plant cell structures

  nucleus- contains DNA

  mitochondria- responsible for aerobic respiration

  cell membrane-controls what enters and leaves the cell

  ribosomes-protein synthesis

  cytoplasm- chemical reactions

  chloroplasts- contain chlorophyll which are the site of photosynthesis

  vacoule- contains cell sap

  cell wall- made of cellulose, provides structure and strength for cell
• bacteria cells are prokaryotic cells, they do not have a nucleus, they have freefloating dna, plasmid loops, cytoplasm, cell membrane and flagella.
• prokaryotic cells (bacteria)- simpler, smaller, no nucleus

  eukaryotic cells (plant and animal cells)- bigger, more complex, have a nucleus
• specialised cells

  sperm cell-contains acrosome, enzymes help break down egg cell, mitochondria give energy to reach egg cell, tail for movement

  egg cell- nutrients in cytoplasm, membrane changes structure to stop multiple sperm getting in
• mitosis is the process of cell division that results in two identical daughter cells, it is important for growth and repair.
• interphase-dna replication

  prophase-nucleus break down and spindle fibres form

  metaphase- chromosomes line up in middle of cell

  anaphase- spindle fibres move chromatids away to each end of the cell

  telophase- nucleus reforms

  cytokenesis- cytoplasm splits creating 2 daughter cells
• Mutations in the DNA can cause mitosis to happen uncontrollably, leading to cancer
• Growth means the increase in the size of an organism or the increase in the number of individuals of a species. Plants elongate and divide to grow. animal cells typically just divide.
• Percentile charts measure growth. 100th percentile- well above average, 50th percentile- average, 10th percentile- below average. It is a way of comparing organisms growth.
• Stem cells are unspecialised cells that can differentiate into specialised cells. There are 3 types of stem cell, embryonic stem cells can turn into any type of stem cell in a human, animal stem cell are already partially specialised so can only turn into certain types of cell. This is because animals stop growing so do not need to create new cells. Plants have meristem cells- can turn into any type of stem cell in a plant.
• Stem cells can be used to treat diseases such as diabetes and paralysis. If we stimulate them to produce the cells we need, we can help cure and fix certain diseases.
• Problems with stem cells

  They can continue to divide and create a tumour, the bodies immune system can reject cells killing it off.
• The nervous system is the way that the body sends and receives information. It is made up of the brain, spinal cord and nerves. There are two parts, the central nervous system is made up of brain and spinal cord, and the peripheral nervous system is made up of all the other neurones.
• There are 3 different types of nerve cell: sensory neurones, motor neurones and relay neurones. Sensory neurones consist of dendron, axon, dendrites and axon terminal. Sensory neurones are connected to the receptors, they take in surroundings through our senses, all sensory neurones are in the peripheral nervous system
• Motor neurones have an axon but no dendron, dendrites are directly on the cell body, we still have our axon terminals. Motor neurones carry impulses to our effectors (muscles or glands). Relay neurones are short neurones found in the brain and spinal cord, look exactly like motor neurones.


  These are the labels. myelin sheath- yellow bits- cover neurones , insulate them and speed up impulses.

  
• Impulse begins with stimulus, receptors pick this stimulus up, the stimulus travels through all the different neurones and through the brain, connects to our effector (muscle or gland), signifies a response


  diagram:

  
• Synapse - gap between one neurone and another, chemical messenger released by presynaptic membrane diffuses across synapse and binds to receptor site on postsynaptic membrane, causes depolarisation which triggers new action potential down next neurone. This happens at every junction between neurons.
• Between each neurone, there are small gaps called synapses. They are 20nm wide, and are filled with chemicals called neurotransmitters. Neurotransmitters are released from axon terminals and diffuse across the synapse to the dendrites of the next neurone. New impulse is generated at every neuron so the signal doesn't lose strength.
• Cerebrum makes up the main bulk of the brain, divided into 2 hemispheres, 4 lobes, cerebellum is responsible for motor functions such as walking, medulla oblongata is responsible for unconscious processes such as breathing or controlling heart rate.


  diagram:

  
• red blood cell- transport oxygen around the body, no nucleus so more room to carry oxygen, contains a red pigment called haemoglobin that binds to oxygen molecules, flat bi concave disk shape to increase surface area to volume ratio

  muscle cell- contract and relax to allow movement, contains protein fibres which can contract to make cells shorter, contain lots of mitochondria to release energy from respiration, allowing the muscles to contract.
• nerve cell- carry electrical impulses around the body, branched endings called dendrites to make connections with other neurones or effectors, myelin sheath insulates the axon to increase transmission speed of the electrical impulses
• root hair cell- absorb mineral ions and water from the soil,long projection speeds up the absorption of water and mineral ions by increasing the surface area of the cell, lots of mitochondria to release energy for the active transport of minerals ions from the soil

  palisade cells- enable photosynthesis in the leaf, lots of chloroplasts containing chlorophyll to absorb light energy, located in the top surface of the leaf where it can absorb the most light energy
• diffusion is the spreading out of particles from an area of high concentration to an area of low concentration

  factors that affect the rate of diffusion: difference in concentration, temperature and surface area of the membrane
• osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane, water moves from an area of lower solute conc to an area of higher solute conc
• examples- nutrients in the small intenstine diffuse into the capillaries through the villi, oxygen diffuses from the air in the alveoli into the blood in the capillaries, carbon dioxide diffuses from the blood in the capillaries to the air in the alveoli, urea diffuses from cells into the blood for excretion in the kidney, carbon dioxide used for photosynthesis diffuses into the leaf through the stomata, oxygen produced during photosynthesis diffuses out of the leaves through the stomata
• Natural selection

  Survival of the fittest - animals that are better suited to the environment survive and those that are not die off
• Stages of natural selection

  1. Variation

  2. Natural selection

  3. Inheritance

  4. Evolution
• Variation


  • Naturally occurring differences within a species due to genetics and environment
• Evolution


  • Animals not suited to the environment die off, leaving the adapted ones to survive and reproduce
• Darwin and Wallace came up with the theory of evolution
• Evidence for evolution

  • Bacteria developing antibiotic resistance
  • Human fossils showing gradual changes
  • Pentadactyl limb in different animals
• Five kingdoms to classify living things

  • Animals
  • Plants
  • Fungi
  • Prokaryotes
  • Protists
• Three domain system

  • Archaea
  • Bacteria
  • Eukarya (complex multicellular organisms)
• Selective breeding

  Breeding parents with desired characteristics to produce offspring with those traits
• Selective breeding can reduce the gene pool and cause health problems
• Tissue culture

  Growing cells on a medium to clone plants or create specialized animal cells
• Genetic modification

  1. Extract gene from one organism

  2. Insert gene into plasmid vector

  3. Insert plasmid into target organism cell