Cells

Use the terms 'eukaryotic' and 'prokaryotic' to describe types of cells

• Eukaryotic cells are the collective names for all animal cells (including human beings), plant cells, fungi cells, and protista cells.

• Prokaryotic cells are the collective name for all bacteria.

Describe the features of bacterial (prokaryotic) cells

• cytoplasm - a liquid gel in which the organelles are suspended and where most of the chemical reactions needed for life take place.

• cell membrane - controls the passage of substances such as glucose and mineral ions into the cell. It also controls the movement of substances such as urea or hormones out of the cell.

• DNA loop - Genetic material that is not in a distinct nucleus.

• Plasmids - extra small rings of DNA often used as a vector in genetic modification

Demonstrate an understanding of the scale and size of cells and be able to make order of magnitude calculations, in standard form

• magnification example = X2000

• size example = 1 micrometre = 1000 nanometres 

• standard form example = 4.32 x 10⁴

Recall the structures found in animal and plant (eukaryotic) cells in algal cells

Animal Cells

• Nucleus
• Cytoplasm
• Cell membrane
• Mitochondria 
• Ribosomes

Plant cells

• Nucleus 
• cytoplasm
• Cell membrane
• Mitochondria
• Ribosomes
• cellulose cell wall
• chloroplast 
• a permanent vacoule

Describe the functions of the structures in animal (eukaryotic) cells

• Nucleus - controls all the activities of the cell and is surrounded by the nuclear membrane. It containse genes on the chromosomes that carry the instructions for making proteins.

• Cytoplasm - A liquid gel which the organelles are suspended and where most of the chemical reactions needed for life take place.

• Cell membrane - controls the passage of substances such as glucose and mineral ions into the cell. it also controls movement of substances such as urea or hormones out of the cell.

• mitochondria - structures in the cytoplasm where aerobic respiration takes place, releasing energy for the cell.

• Ribosomes - where protein synthesis takes place, making all the proteins needed in the cell.

Describe the functions of the structures in plant (eukaryotic) cells

(plant cells also have the structures described in (animal cell) 

• cellulose cell wall - stregnthens and supports the cell

• Chloroplasts - These are found in all the green parts of the plant. They are green because the contain chlorophyll which absorbs light so the plant can make food by photosynthesis.

• Permanent vacuole - space in the cytoplasm filled with cell sap for keeping the cells rigid to support the plant.

Describe what a specialised cell is, including examples for plants and animals 

As an animals cell differentiates to form a specialised cell it aquires different sub-cellular structures to enable it to carry out a certain function. (e.g. muscle cells, or nerve cells)

Plant cells may be specialised to carry out a particular function within tissues, organs, organ systems, or whole organisms. (e.g. root hair cells, xylem cells, phloem cells, photosynthetic cells)  

Describe what differentiation is, including differences between animals and plants 

differentiation is the process where cells become specialised for a particular function.

In the early developement of an animal, the cells are unspecialised. Each of them are known as stem cells and have the ability to become any type of cell that is needed. The cells can make nerve cells, muscle cells, ect. However, if there are cells like red blood cells and skin cells, that cannot divide at all, adult stem cells can replace the dead or damaged cells.

In plants most of there cells are able to differentiate all through their lives. Undifferentiated cells form at active regions of the stem and roots known as the meristem. Then they go through mitosis for cell division, elongate and then grow before actually differentiating. Even after this though differentiation is not permanent if you moce a plant cell from one part to another it can redifferentiate.

Define the terms magnification and resolution

Magnification on a microscope refers to the amount or degree of visual enlargement of an observed object.

magnification = image size / size of real object 

Resolution is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible (able to be seen or noticed) change in the reading.

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

Light microscopes magnify up to about X2000 and have a resolving power of about 200nm

Electron microscopes magnify up to about X2,000,000 and have a resolving power of around 0.2nm.

1nm = 1 x 10^-9m  or 0.000,000,001m

Bio ONLY: Describe how bacteria reproduce and the conditions required

Bacteria reproduce / divide rapidly and easily by simple cell division (Binary fission).

To do this  they need a supply of nutrients and usually find this in moist, protein-rich foods. They need moisture, without moisture, the growth of bacteria slows down and may stop. In experiments, they are normally grown at a temperature of 25^oC.

Bio ONLY: Describe how to prepare an uncontaminated culture

An uncontaminated culture of microorganisms can be grown using sterilised Petri dishes and agar.

You sterilise the innoculating loop before use and fix the lid of the Petri dish to prevent unwanted microorganisms getting in.

Bio ONLY: Calculate cross-sectional areas of colonies or clear areas around colonies using πr²

To calculate the cross-sectional areas of each colony would be pi x radius².

For example: if an area of colonies have a radius of 2cm, the area would be 12.57cm²  or 1.257 x 10¹cm

Bio ONLY: Calculate the number of bacteria in a population after a certain time if given the mean division time

number of bacteria in a population = bacteria at the beginning of the growth period x 2^{number of divisions}

Example:

The mean division time for a population of bacteria is 30 minutes. Calculate how many bacteria will result from each individual bacterium after 8 hours.

If the bacteria divide every 30 minutes, they will divide twice an hour. If it is in 8 hours it will divide 16 times

number of bacteria at the beginning = 1

number of divisions = 16

number of bacteria at the end of the growth period = 1 x 2¹⁶ = 65,356 or 6.5356 x 10⁴ bacteria

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

You can add circles of filter paper soaked in different types of concentrations of disinfectant or antibiotic when you set up the culture plate. An area of clear agar gel indicates that the bacteria have been killed or cannot grow. This zone of inhibition can be measured and used to investigate the effect of different antiseptics or anitbiotics on the growth of the bacteria

Describe how genetic information is stored in the nucleus of a cell (inc genes & chromosomes)

Each cells in the body has a nucleus that contain chromosomes, each of these chromosomes (that come in two pairs in each nucleus) carry the genes that contain the instructions for making both new cells and all the tissues and organs.

A gene is a small packet of information that controls a characteristic, or part of a characteristic, of your body. It is a section of DNA, the unique molecule that makes up your chromosomes.

Describe the processes that happen during the cell cycle, including mitosis (recognise and describe where mitosis occurs)

1. Longest stage in the cell cycle. The cell grows bigger, increase their mass, and carry out normal cell activities. Most importantly they replicate their DNA to form two copies of each chromosome ready for cell division. They also increase the number of sub-cellular structures such as mitochondria, ribosomes and chloroplasts ready for the cell to divide.

2. Mitosis: in the process one set of chromosomes is pulled to each end of the dividing cell and the nucleus divides.

3. The stage during which the cytoplasm and the cell membranes also divide to form two identical daughter cells. 

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

Embyronic stem cells (from human embryos) and adult stem cells (from adult bone marrow) can be cloned and made to differentiate into many different types of cell.

Treatment with stem cells may be able to help conditions such as paralysis and diabetes.

Stem cells from plant meristems are used to produce new plant colens quickly and economically for reasearch, horticulture, and agriculture.

• Animal stem cells usually differentiate at the early stages of their life
• Stem cells in adult animals are mainly used for replacement or repair
• Plant cells differentiate throughout their life cycle
• Plant stem cells are grouped together in structures called meristems

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

a modern technique for cloning plants is tissue culture using small groups of cells taken from part of a plant to grow identical new plants. It is important for preserving rare plant species in nurseries as well as for commecial use.

In theraputic cloning, an embryo is produced with genes as the patient so the stem cells produced are not rejected and may be used for medical treatment.

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

benefits:
stem cell research is being carried out into potential therapies to treat:

• spinal cord after injuries
• diabetes
• heart after damage in a heart attack
• eyesight in the blind
• damaged bone and cartilage

risks:

• Many embryonic stem cells are from aborted embryos.
• Many poeple have ethical and religious objections
• embryonic stem cells has been relatively slow, difficult, expensive, and hard to control.

Describe the process of diffusion, including examples Explain how diffusion is affected by different factors

Diffusion is the spreading out of particles of any substance, in solution or a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration, down a concentration gradient.

The rate of diffusion is affected by the difference in concentrations, the temperature, and the available surface area.

Dissolved substances such as glucose and urea and gases such as oxygen and carbon dioxide move in and out of cells by diffusion. 

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

Single-celled organisms have a relatively large surface area to volume ratio so all necessary exchanges with the enviroment take place over this surface.

In multicellular organisms, many organs are specialised with effective exchange surfaces.

Exchange surfaces usually have a large surface area and thin walls, which give short diffusion distances. In animals, exchange surfaces will have an efficient blood supply or, for gaseous exchange, be ventilated. 

Explain how the effectiveness of an exchange surface can be increased

The effectiveness of an exchange surface can be increased by:

• Having a large surface area over which exchange can take place.
• Having a thin membrane or being thin to provide a short diffusion path
• In animals, having an efficient blood supply moves the diffusing substances away from the exchange surfaces and maintains a steep concentration (diffusion) gradient.
• In animals, being ventilated makes gas exchange more efficient by maintaining steep concentration gradients.

Describe the process of osmosis (inc calculation of water uptake & percentage gain and loss of mass of plant tissue)

Osmosis is a speical case of diffusion. It is the movement of water from a dilute to a more concentrated solution through a partially permeable membrane that allows water to pass through. 

Differences in the concentrations of solutions inside and outside a cell cause water to move into or out of the cell by osmosis.

Animal cells can be damaged if the concetration outside the cell changes dramatically.

Osmosis can also help plants become Turgid(normal) or if there is less water intake flacid or if more water is lost by osmosis it will become plasmolysed. 

Isotonic, Hypertonic, and hypotonic

Isotonic - this is when the concentration of solutes in the solution outside the cell is the same as the internal concentration.

Hypertonic - this is when the concentration of solutes in the solution outside the cell is higher than the internal concentration.

Hypotonic - this is when the concentration of solutes in the solution outside the cell is lowert than the internal concentration.

Describe the process of active transport, including examples - gut and roots

Active transport moves substances from a more dilute solution to a more concentrated solution against a concentration gradient

Thefore active transport uses energy released form food in respiration to provide the energy required.

Active transport allows plant root hairs to absorb mineral ions required for healthy growth from very dilute solutions in the soil against a concentration gradient

Active transport enables sugar molecules used for cell respiration to be absorbed from lower concentrations in the gut into the blood where the concentration of sugar is higher.

Explain the differences between diffusion, osmosis and active transport

diffusion is the spreading out of any substance in solution or gas, resulting in a net movement from an area of higher concentration to an area of lower concetnration, down a concentration gradient.

Osmosis is the movement of water from a dilute to a more concentrated solution through a partially permeable membrane. 

Active transport is the movement of substances from a more dilute solution to a more concentrated solution against a concentration gradient.

meiosis

meiosis - when a normal diploid cell divides to make 4 non-identical haploid cell:

• each chromosome first makes a copy of itself
• Then the pairs of chromosomes line up together and the cell divides
• then the two cells immediately divide again producing 4 cells each with a single set of chromosomes.

Sperm cells:

• Function is to fertilise an egg.
  • Streamlined with a long tail to swim to the egg.
  • Acrosome in the head containing enzymes to digest the egg cell membrane.
  • Large number of mitochondria in the mid-section to release energy for movement.

Nerve cells:

• Function is to carry electrical signals.
  • Long to carry signals long distances.
  • Branched connections to connect to other nerve cells and form a network around the body.
  • Insulating sheath to enhance transmission of electrical signals.

Onion cell experiment 

• Equipment: Microscope, glass slides, coverslip, scalpel (sharp knife), iodine or stain, microscope

• Procedure:
  • Cut a section of onion and peel of the epidermis (thin inner layer)
  • Place the specimen onto slide.
  • Stain the specimen using iodine.
  • Gently lower cover slip onto the specimen without trapping air bubbles.
  • Soak up any excess liquid with a paper towel.
  • Switch on the light source or move the mirror and place your slide on the stage.
  • Use the lowest objective lens and turn the focusing wheel to move the lens close to the slide.
  • Slowly adjust the focusing wheel until you can see a clear image.
  • Increase the magnification by changing the objective lens and re-focus.

• mitosis is important because 
  • Repairs cells
  • Replace cells
  • Mitosis is how new cells are formed 
  • Two daughter cells formed are clones of the original cell, to keep the same favourable characteristics as the parent

Advantages and Disadvantages of plant stem cells

• Advantages:
  • Rare species can be cloned
  • Crop plants with useful features can be cloned (allow specific examples)
• Disadvantages:
  • Some rare species may compete with crop plants or economically useful plants
  • Cloned plants may be susceptible to disease due to identical genes

• Osmosis in potato tissue
• Use a cork borer to cut potato cylinders of the same diameter.
• Trim the cylinders so that they are all the same length.
• Accurately measure and record the length and mass of each potato cylinder.
• Measure 10 cm³ of the 0.5 M salt solution and put into the first boiling tube.  Label boiling tube as: 0.5 M salt.
• Measure 10 cm³ of 0.25 M salt solution and put into the second boiling tube.  Label boiling tube as: 0.25 M salt.
• Measure 10 cm³ of the distilled water and put into the third boiling tube.  Label boiling tube as water.
• Add one potato cylinder to each boiling tube.  Make sure you know the length and mass of each potato cylinder in each boiling tube.
• Leave the potato cylinders in the boiling tubes for an hour/ overnight in the test tube rack.
• Remove the cylinders from the boiling tubes and carefully blot them dry with the paper towels.
• Re-measure the length and mass of each cylinder.