Biology Paper 1

Required practical 1: use a light microscope to observe, draw and label a selection of plant and animal cells

Using an onion:

• Peel off epidermal layer  on onion using forceps

• Mount onto microscope slide with drop of water using a pipette which makes sure that the tissues lie flat

• Add 2 drops of iodine solution to stain the cell (highlights subcellular structures)

• Place cover slip on slowly so no air bubbles are trapped

• Place the microscope slide in the centre of the stage then focus the slide

• Record an image and rotate the objectives so that the high power objective is in line with the stage

How are sperm cells specialised?

• Sperm cells are specialised to get the male DNA to the female DNA

  • Long tail and streamlined head to help it swim to the egg

  • Lots of mitochondria to provide energy needed for swimming

  • Carries enzymes in its head to digest through the egg cell membrane

How are nerve cells specialised?

• Nerve cells are specialised to carry electrical signals from one part to another part of the body

  • Long cells to cover more distance

  • Branched connections at their end to connect to other nerve cells to form a network throughout the body

How are muscle cells specialised?

• Muscle cells are specialised to contract quickly

  • The cells are long - more space to contract

  • Lots of mitochondria to generate the energy needed for contraction

How are root hair cells specialised?

• Root hair cells are specialised for absorbing water and minerals

  • Grows into long “hairs” that stick out into soil - give the plant big surface area to absorb water and mineral ions

How are phloem and xylem cells specialised?

• Phloem and xylem cells are specialised for transporting substances

  • Phloem and xylem cells form phloem and xylem tubes which transport substances such as food and water around plants.

  • To form the tubes, the cells are long and joined end to end. Xylem cells are hollow in the centre and phloem cells have very few subcellular structure so more stuff can flow through them

Define differentiation and include their differences between animals and plants

Differentiation is the process in which a cell changes to become specialised for its job. In most animal cells, the ability to differentiate is lost at an early stage after specialization. However lots of plant cells don’t ever lose this ability

Define the terms magnification and resolution

Magnification - making something look bigger Resolution - the ability to distinguish two points. Higher resolution, sharper image

Compare electron and light microscopes in terms of their magnification and resolution

Electron: Uses electrons to form an image. Higher magnification and resolution so one can see subcellular structures such as ribosomes and plasmids, or look at them in more detail e.g mitochondria and chloroplast. However costly, hard to use, black and white only and specimen cannot be living Light: uses light and lenses to form an image. Lower resolution and magnification than electron microscope. Can identify individual cells and large subcellular structures eg nuclei

Bio ONLY: Describe how bacteria reproduce and the conditions required

Bacteria can reproduce via binary fission which works best in a warm and moist environment with lots of nutrients. Circular DNA and plasmids replicate Cell gets bigger and circular DNA strands move to opposite ends of the cell Cytoplasm divides and new cell walls form Cytoplasm divides and two daughter cells produced

Bio ONLY: Describe how to prepare an uncontaminated culture

1. Petri dishes and culture medium must be sterilised before use, such as heating to a high temperature, to kill any unwanted microorganisms that may be lurking on them

2. If an inoculating loop is used to transfer bacteria to culture medium, it should be sterilised first by passing it through a hot flame

3. After transferring bacteria, Petri dish lid should be lightly taped on to stop microorganisms from the air getting it

4. Petri dish should be stored upside down to stop drops of condensation falling onto agar surface

Required practical 2: investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zones of inhibition

1. Place paper discs soaked in different types or concentrations of antibiotics on an agar plate that has an even covering of bacteria. Leave some space between discs

2. The antibiotic should diffuse into agar jelly. Antibiotic resistant bacteria will continue to grow on the agar around the paper disc, but non-resistant strains will die. Clear area will be left where bacteria have died, known as the inhibition zone

3. Use a control: paper disc that has not been soaked in the antibiotic. Instead soak it in sterile water. This is to make sure that any difference between the growth of the bacteria around the control discs and around one of the antibiotic discs is due to the effect of the antibiotic alone

4. Leave plate for 48 hours at 25 degrees

5. The more effective the antibiotic is, the larger the inhibition zone

Describe the processes that happen during the cell cycle

The cell cycle makes new cells for growth, development and repair, used by multicellular organisms

Growth and DNA replication

1. In a cell that’s not dividing, DNA spread out in long strings

2. Before division, cell has to grow and increase the amount of subcellular structures like mitochondria

3. DNA duplicates - one copy for each new cell. DNA copied and forms X-shaped chromosomes in which both arms of the chromosome have the same DNA

Mitosis

4. Chromosomes line up at the centre of the cell and cell fibre pushes them apart. Two arms of each chromosome go to opposite ends of the cell

5. Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells as the nucleus has divided

6. Cytoplasm and cell membrane divide which produces two new daughter cells

Describe stem cells, including sources of stem cells in plants and animals and their roles

Stem cells are undifferentiated cells.

Animal stem cells

Animal stem cells can be grown in a lab to produce clones and made to differentiate into specialized cells to use in medicine and research.

Embryonic stem cells can differentiate to any type of specialised cell.

Adult stem cells can only differentiate into different types of blood cells. They are found at the bone marrow
Plant stem cells

Plant stem cells are found in the plant’s meristem which is there throughout the plant’s entire life

Describe the use of stem cells in the production of plant clones and therapeutic cloning

Plant cloning:

• The stem cells can be used to produce clones which means more plants of rare species can be grown

• Stem cells can also be used to grow crops of identical plants that have desired features for farmers e.g disease resistance

Therapeutic cloning:

• Embryonic stem cells can carry out therapeutic cloning where an embryo could be made to have the same genetic information as the patient won’t be rejected by the patient’s body if used to replace faulty cells such as pancreatic cells, nerve cells and misshaped red blood cells caused by sickle cell anemia

• How this is done: extract embryonic stem cells from early embryos. Grow them in a laboratory. Stimulate them to differentiate into any type of specialised cell we desire. Give them to the patient to replace their faulty cells

Discuss the potential risks, benefits and issues with using stem cells in medical research/treatments (inc diabetes and paralysis)

General drawback for animal stem cells:

• Stem cells that are grown in a lab may become contaminated with a virus which could be passed on to the patient

• Tumour development - cells can grow out of control once they’ve been transplanted which can cause a cancer to grow

Embryonic stem cells

1. Limited supply and ethical issues

2. Patient’s immune system may reject their stem cells

3. Tries to destroy if they are seen as foreign

But can reduce the risk by giving the patient medication to help suppress their immune system (doesn’t always work and can have some bad effects!!)

Adult stem cells

1. Won’t cause rejection

2. But can help with sickle cell anemia, not diabetes or paralysis

Describe the process of diffusion, including examples

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. It happens in the cell membranes where only small molecules like oxygen, glucose and water can diffuse but not starch or proteins (big)

Explain how diffusion is affected by different factors

Higher conc gradient (conc difference) = higher diffusion rate

Higher temp = more energy = more faster = higher diffusion rate

Define and explain "surface area to volume ratio", and how this relates to single-celled and multicellular organisms (inc calculations)

Surface area to volume ratio is how easy it is for an organism to exchange with its environment Single celled organisms - large surface area to volume ratio so gases and dissolved substances can diffuse directly into/out of the cell across cell membrane Multicellular organisms - smaller SA:V ratio - not enough substances can diffuse to supply their entire volume so they need exchange surfaces to allow enough necessary substances to pass through, increasing diffusion efficiency

Explain how the effectiveness of an exchange surface can be increased

Exchange surfaces are adapted to maximise effectiveness:

• Thin membrane - short diffusion pathway

• Large surface area - increased diffusion

• Lots of blood vessels in animals - stuff gets in and out of blood fast

• Gas exchange surfaces in animals often ventilated, so air moves in and out

Explain how lungs are useful for their adaptation

1. Lungs - transfer oxygen to the blood and remove waste CO2 from it. Has alveoli where gas exchange takes place

   1. It has a huge surface area, moist lining for dissolving gases, very thin walls (1 cell thick) and a good blood supply

Explain how small intestine is useful for its adaptation

1. Small intestine - villi - 1 cell thick so fast diffusion - increases SA so much that digested food is absorbed much more quickly into blood. It also has a very good blood supply for quick absorption

Explain how leaves are useful for their adaptation

1. Leaves - CO2 diffuses into air spaces within leaf then diffuses into cells where photosynthesis happens

   1. stomata - where CO2 diffuses. Size of stomata controlled by guard cells which lose the stomata if the plant loses water faster than it is being replaced by roots - without these the plant would soon wilt. 

   2. The flattened shape of the leaf increases the surface area so it's more effective. Walls of cells have air spaces inside the leaf which increase the area of surface so more CO2 can get inside cells.

   3. Water vapour evaporates from cells inside the leaf. It escapes by diffusion since a lot of t is inside the leaf and less of it in air outside

Explain how gills are useful for their adaptation

1. Gills - water enters fish through its mouth and passes out through gills. As this happens, oxygen diffuses from water into blood in gills and CO2 diffuses from blood into water

   1. Each gill is made of gill filaments which give a big surface area. 

   2. They are covered in lamellae - tiny structures which also increase SA. 

   3. They also have lots of blood capillaries to speed up diffusion

   4. Thin surface layer of cells to minimise diffusion distance

   5. Blood flows through lamellae in one direction and water flows over in opposite directions. This maintains a large concentration gradient between water and blood

   6. Conc of oxygen in water > conc of oxygen in blood so as much oxygen as possible diffuses from water into blood

Required practical 3: investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue

1. Cut equal size cylinders from potato and remove skin (non-permeable). Remove excess water from surface and weigh using top-pan balance

2. Place each cylinder in test tubes with different concentrations of sugar solution and leave for a set time (i.e 1 day). Water will move in or out of cells due to osmosis

3. Remove cylinders, dab off excess water reweigh and calculate based on this formula: 

4. % change in mass = final mass - initial massinitial mass*100

5. Plot this against concentration. When line of best fit meets X-axis, this is the concentration of potato as there would be no net movement of water in/out

What would be the independent, dependent and control variables for the osmosis experiment?

Independent: conc of sugar solution

Dependent: % change in mass

Control: same size/shape of cylinders, time, volume of solution, same vegetable

Describe the process of active transport, including examples

Active transport is the movement of substances from a lower to higher concentration. It goes against the concentration gradient and require energy

• Root - has loads of hairs which gives the plant large SA for water and mineral ion (for healthy growth) absorption from soil. But the concentration of minerals is usually higher in root hair cells than in the soil around them, so root hair cells cannot use diffusion

• Active transport allows the plant to absorb minerals from a very dilute solution against  concentration which is essential for its growth. But requires energy from respiration to make it work

• Gut - diffusion cannot take place if there’s lower concentration of nutrients in the gut than there is in the blood which means conc gradient goes wrong way. 

• Active transport allows nutrients to be taken in the blood even if the conc gradient is the wrong way. 

• But now glucose can be taken into the bloodstream when its concentration in the blood is already higher than in the gut. It can be transported to cells where it’s used for respiration

Explain the differences between diffusion, osmosis and active transport

Diffusion		Osmosis		Active Transport
High to low concentration		High to low concentration		Low to high concentration
No energy		No energy		Requires energy as it moves against concentration gradient
No membrane required		Membrane required (partially permeable)		Membrane required (protein carrier)
Substances: gases, liquids and dissolved solutes		Substances: water only		Substances: ions, glucose and mineral ions