biology paper 1

• chloroplasts


  contain a green pigment called chlorophyll that is the site of photosynthesis
• mitochondria


  where aerobic respiration happens
• cell membrane


  controls what goes in and out of the cell
• nucleus


  contains genetic material (DNA)

  controls the cell
• permeable vacuole


  contains cell sap

  gives the leaf it's shape
• xylem cells - specialised cell

  • found in the plant stem and can form long tubes
  • these long tubes help carry minerals + water from the roots to the leaves.
  • have thick walls containing lignin which provide support to the plant
  • as a result of the walls being sealed with lignin the xylem cells die
  • the end wall between the cells are completely broken down.
  • this means that cells can form long tubes so that minerals + water can flow easily
  • xylem cells have no: nucleus, chloroplasts, vacuole, cytoplasm
  • it has no internal feature which makes it easier for water + minerals to flow easily.
• phloem transports


  amino acids + sucrose
• total magnification equation


  total magnification = eye piece lens x objective lens
• bacteria


  are unicellular (only consist of a single cell).
•   states can molecules diffuse

  gas and liquid
• Which molecules are able to diffuse into and out of cells

  water

  glucose

  amino acids
• magnification

  how many times larger the image is than the actual object
• Diffusion

  the spreading out of particles which results in a net movement from a high concentration to a low concentration.

  Particles move down the concentration gradient
• adaptations of the lungs that help the rapid absorption of oxygen into the blood.

  • membrane of alveoli has a large surface area
  • good blood supply
  • many capillaries
  • short diffusion pathway - because membrane is one-cell thick
• villi - adaptations that help it be good for absorption of nutrients

  • network of capillaries
  • thin wall (one cell thick)
  • good blood supply
  • large surface area due to folding
• root hair cells - adaptations for uptake of water and minerals

  • it has a lot of mitochondria to help it take in mineral ions + water via active transport
  • a large surface area helps efficient absorption of mineral ions + water
• FISH GILLS - 


  deoxygenated blood passes into the fillaents

  Oxygen diffuses from the water into the blood

  Oxygenated blood returns into the body
• SURACE AREA TO VOLUME RATIO - SINGLE CELLED ORGANISMS


  single celled organisms such as ameoba can rely on diffusion to transport molecules in and out of the cell
• Required practical - Osmosis potato

  1. Peel the skin off the potato

  2. Use a coke borer to cut them into 3 cylinders to ensure they all have the same diameter

  3. Use a scalpel to ensure that they are all the same length (3mm)

  4. Measure the length using a ruler and the mass using a balance

  5. Place the cylinders in a test tube

  6. Add 10cm^3 of 0.5 molar sugar solution to 1st test tube

  7. Add 10cm^3 of 0.25 molar sugar solution to 2nd test tube

  8. Add 10cm^3 of distilled water to 3rd test tube

  9. Leave it in the test tubes overnight so osmosis can take place

  10. Take it gently out of the test tube then roll it on a paper towel to get moisture off the surface (don't squeeze it)

  11. Measure the length and mass again

  12. Calculate the percentage change
• Peeling the skin off the potato can affect the rate of osmosis
• Don't use tap water because it has dissolved substances in it and this could affect the rate of osmosis
• Osmosis taking place in potato

  In water the potato cylinder will gain mass as water has moved IN by OSMOSIS

  In a consecrated solution the cylinder will shrink as it has lossed mass due to water MOVING OUT by OSMOSIS.
• OSMOSIS PRACTICAL - GRAPH


  where the line crosses with the X-axis there is no mass change. This means the consecration on the OUTSIDE OF THE CELL is THE SAME as the consecration INSIDE THE CELL.

  
• equation for percentage change - OSMOSIS PRACTICAL

  % change = change in value/ original value x 100
• Examples of gas exchange in humans

  Villi in the small intestines'- absorbs mineral ions, amino acids +glucose and diffuses them into the blood stream.

  alveoli in the lungs- diffuses oxygen + carbon dioxide in and out of the blood stream
• Common Exchange Surfaces in animal and plants

  • good blood supply - maintaining a strong concentration gradient as blood is constantly replaced.
  • large surface area- a lot of molecules can diffuse at the same time
  • surfaces are permeable- lots of substances can push through easily
• Chromosomes


  are made of DNA

  are paired

  Humans have 23 pairs of chromosomes

  Gametes aren't paired

  They have large number of genes - they give use our features
• Mitosis


  is the body cells dividing into identical daughter cells
• why does mitosis happen?

  mitosis helps the growth + repair of multicellular organisms e.g plant and animals (e.g skin cells / breaking a bone

  Used for asexual reproduction

  happens in 3 stages
• STAGES- Mitosis


  1st stage: DNA replicates to form two pairs of chromosomes

  the cell grows bigger

  the sub-cellular structures ribosomes + mitochondria duplicate

  2nd Stage: Mitosis

  chromosomes line up in the middle

  pairs of chromosomes pull to each end of the cell

  the nucleus divides to form 2 nuclei

  3rd Stage: cytoplasm + cell membrane divide to form identical daughter cells
• STEM CELLS 


  are undifferentiated cells that can develop into one or more types of specialized cells

  Stem cells are cloned to produce identical cells
• the main types of stem cells in mammals?

  adult stem cells & embryonic stem cells
• ADULT STEM CELLS


  can be found in bone marrow

  can only differentiate into certain types of specialized cells.

  E.g bone marrow differentiate into types of blood cells
• Advantages of using Adult Stem cells

  • no ethical issues - adults can give consent for when they want their stem cells removed and used
  • used to treat bone marrow cancer e.g leukemia
  • this works by using radiation to destroy the existing bone marrow.
  • the stem cells divide to form new bone marrow and can differentiate into types of blood cells.
  • it is relatively safe treatment and the donor can recover quickly
• disadvantages of adult stem cells

  • they can only treat fewer diseases as they can only differentiate into certain types of specialized cells.
  • there are risks of viruses that can be passed from the donor to the patient
  • the donor has to be compatible with the patient (requires a long wait) - or else the white blood cells from the new bone marrow can attack the patients body.
• embryonic stem cells


  are found in human early embryos and are obtained from spare embryos from the fertility clinic

  they can differentiate into a any type of specialized cell - meaning they can treat many types of diseases
• advantages of embryonic cells

  • a donor is usually not required - they are obtained spare embryos from fertility clinics
  • they can grow whole replacement organs
  • can treat a lot of diseases as they can differentiate into any type of specialised cell.
• disadvantage of embryonic cells

  • ethical issues - embryos are destroyed and are seen as potential human life.
  • Can risk transferring diseases to the patient
  • new treatment - under researched so not clear if they can actual diseases.
• plant meristem


  found in roots and shoots of plants

  can differentiate into all cell types - they can create clones of whole plants
• advantages of meristem

  • rare species can be cloned - to prevent extinction
  • if a plant has a desirable trait (disease resistance) it can be cloned to create a large number of identical plants
  • fast and low cost production for a large number of plants.