B1

CELLZ

All living things are made of cells there are:

Eukaryotic cells- A complex cell with a nucleus and other organelles that are bound by membranes- Usually part of a multicellular organism

Prokaryotic cells- A simple cell without a nucleus- usually a single celled organism

Plant cells have a:

Nucleus- Contains genetic materials that controls the cell

Cytoplasm- Gel-like substance where most the chemical reactions happen

Mitochondria- The site of aerobic respiration making ATP

Cell membrane- Holds the cell together, controls what goes in and out

Ribosomes- The site of protein synthesis

Cell wall - Supports the cell and strengthens it

Permanent vacuole -Contains cell sap, a weak solution of sugars and salts

Chloroplasts- Contains chlorophyll, that absorbs light for photosynthesis

Plasmids- Small rings of DNA

Strand of DNA- Contains genetic information

Microscopy

• Resolution- The quality of the image and ability to distinguish 2 points

• Microscope- An instrument that magnifies small objects so that they can be seen

• Magnification- How zoomed in something is

• Specimen- What you are trying to look at with a microscope

This is usually for particles and objects that can’t be seen with the naked eye, there are two types:

Light microscopes:

• These use light and actual lenses to magnify the specimen

• These let us see individual cells and large subcellular structures like nuclei

Electron microscopes:

• These use electrons to form an image

• These have a much higher magnification and resolution than electron microscopes

• This gives us images of:

  • The internal structure of chloroplasts and mitochondria

  • Plasmids

  • Ribosomes

How to prepare a microscope:

1. Add a drop of water to the middle of a clean slide

2. Prepare your specimen e.g. the epidermal tissue of onions

3. Add a drop of iodine solution to stain the specimen

4. Carefully place a cover slip, in such a way that air bubbles don’t form

5. As they obstruct your view of the specimen

6. Clip the slide prepared onto the stage

7. Select the lowest power objective lens

8. Use the coarse adjustment knob to move the stage just

9. look down the eye piece and adjust the stage until it’s roughly in focus

10. adjust the fine adjustment knob until you get a clear image

11. If needed, adjust to a higher power objective lens

• When drawing your findings draw them clearly, plainly with labels like So’s Dad:

Stem Cells

• These are undifferentiated cells that can divide and differentiate and turn into a selection of many different types of cells.

• Therapeutic cloning is a type of cloning that gives embryonic stem cells the exact same DNA as the patient, reducing the changes of an immune reaction

There are 3 main types:

• In adults they mainly just exist in the bone marrow, and can only turn into certain types of cells e.g. blood cell

• Embryonic stem cells have the ability to truly turn into any type of cell of choice

• And meristems are plant stem cells which are found at roots and shoots and can turn into any type of plant cell

Embryonic stem cells can be used to replace faulty cells in diseases such as:

• Nerve cells with paralysis

• Insulin producing cells with diabetes

• Meristems in plant cloning: can be used to clone and protect endangered or rare species of plants

Risks and issues:

• There are issues of ethnicity of using an embryo which is the potential for life

• However others think the lives it could save come first

• If the embryonic stem cells get infected with a virus then they could make patients sicker

Mitosis

But firstly chromosomes:

Chromosomes Are the 23 pairs of Coiled up lengths of DNA in the nucleus of the cell From an organisms Mother and farther, That controls the organisms Characteristics e.g. Hair colour, height etc, through their many genes

Body cells divide in a process called the cell cycle as part of processes of growth and replacement:

DNA replication and growth:

• This is when the cell increases the amount of all subcellular structures

• An the DNA duplicates and Chromosome forms the following X’s:

  

Mitosis:

• The chromosomes line up at the centre of the cell

• And cell fibres pull the to opposite sides of the cell

• These become the

Cell adaptation

• Differentiation- The process of a cell changing into a specialised cell that preforms a specific task

• Specialised cell- A cell adapted to preform a specific function in the body

• Stem Cell- An undifferentiated cell

In an animals the ability to differentiate into any type of cell is lost as they reach maturity, and differentiation is mainly used to repair damages skin or blood cells.

Specialised cells include

• Sperm cells-

  • Their function is to get the male DNA to the female DNA

  • So they have a streamlined head and long tail to help it swim

  • They have lots of mitochondria to provide it with energy

  • They have enzymes to digest through the egg cell membrane

• Nerve cells-

  • Their function is to carry electrical signals

  • So they are long to cover more distance

  • And have branched connections at their end to form more networks

• Muscle cells-

  • Their function is to contract quickly

  • They are long so they have space to contract

  • They have lots of energy to provide energy for contraction

• Root hair cells-

  • These have absorb water and mineral ions form plants

  • So have a large SA: V ratio for absorbing water and mineral ions

• Phloem and xylem cells

  • These are Mostly hollowed out to allow the transport of substances

  • And have very few subcellular structures to avoid obstruction of transport

Binary fission

This is how prokaryotic cells reproduce

• The circular DNA and plasmids replicate

• The cells get bigger and the DNA strands move to opposite poles

• The cytoplasm divides

• And two daughter cells are produced with circular strands of DNA and a variable amount of plasmids

In a warm environment with lots of nutrients some bacteria e.g. E-coli can take 20 mins to replicate. In bad conditions however they stop dividing and die out

Bacteria need food (carbohydrates, proteins, minerals etc), water, oxygen, suitable temperature and a suitable Ph (preferably neutral) to grow

Culturing Microorganisms

Bacteria (and other things) can be cultured using a culturing medium - which can be a nutrient broth solution or agar jelly which allows bacteria to grow in a petri dish:

At school labs the temp has to be under 25^oc to stop harmful pathogens from growing

But this rule is bypassed on an industrial scale to make the process faster.

You can prepare the thing above by:

1. Pouring hot agar jelly into a petri dish

2. Use a sterile inoculating loop to get an even spread of bacteria

3. Then let it multiply

After this you can place different disks that were soaked in a certain disinfectant into the bacteria culture. And leave them to kill non-resistant strains of bacteria to see which disinfectant is strongest by which one has the largest area of inhibition

You can find the area of inhibition zones to compare effectiveness and you can find the area of bacteria covered.

Area = πr²

Aseptic technique:

1. Heating the petri dish to sterilise it beforehand

2. Passing inoculating loop through hot fire

3. Tapping petri dish lightly to let air through

4. Storing petri dish upside down to prevent condensation falling on agar jelly

Diffusion , Osmosis and active transport

Diffusion is the movement of particles from an area of higher concentration to lower concentration

- Takes place in liquids and gasses

Factors that increase rate of diffusion

• High Temperatures- Particles have more energy to move faster, generating greater net movement

• Steep concentration gradient- The greater the difference in particle concentration between areas

• Diffusion distance- Less distance to travel means faster diffusion

• Surface area- Higher SA == faster diffusion, allows passage of more molecules at a given time

Cell membranes use diffusion

Via transporting substances quickly to maintain a steep concentration gradient and allowing the substance they want in through the cell membrane, Whilst being designed with a high surface area: e.g.: Villi + Alveoli

Osmosis

• Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of low concentration

• This movement is usually chaotic however has a net movement (overall movement) which shows an overall movement of water.

• A strong sugar or salt solution will have the lower water concentration

Practical

1. Cut potatoes into identical cylinders

2. Measure their mass

3. Add them to a 0.2 mol/dm³ solution sugar

4. Take it out after x mins

5. Dry off excess water

6. Measure it’s mass

7. Repeat steps 2-6 with a different concentrations,

8. Record percentage change

Active transport

This is the movement of substances against the concentration gradient using energy form respiration

Sped up by a greater surface area and used in root hair cells:

• They have a large surface area for absorbing mineral ions

However things need energy from respiration to use active transport

Active transport happens in the gut when there is more glucose in the gut than the blood but usually the concentration gradient favours the gut meaning that glucose naturally enters is via diffusion

Exchange

• An exchange surface is a plane on which substances move across.

• The larger the surface area to volume ratio is, the quicker exchange of substances happen

Exchange surfaces adaptations are:

• Thin membranes-( Lowers exchange distance)

• Large surface area- So lots of substance can diffuse at once

• Good blood supply- To get things in and out the blood quickly

• Ventilation- For space to diffuse in for gasses

Adapted organs are:

• Leaves

• Small intestines

• Large intestines

• Lungs

• Root hair cells

• Gills

Lungs~

• Their job is to get oxygen in the blood and CO₂ out

• They do this with millions of tiny air sacs called alveoli with~

  • Good blood supply

  • Very thin lining

  • Large surface area (Roughly 75m²)

  • Moist lining- For dissolving gases

Small intestines

• These have millions of tiny projections called villi which absorb digested food into the bloodstream

• They have:

  • Very good blood supply

  • Thin single celled lining

Leaves:

• Stomata

  • At the bottom as to not interfere with palisade mesophyll tissue

  • Controlled by guard cells

  • Air spaces in the leaf increase SA:V ratio

  • flattened shape increases SA:V ratio

Gills:

• Water (containing oxygen) enters through gills

• Oxygen diffuses from water into blood in the CO₂

• Gills covered in gill filaments covered un lamellae, Increases SA:V ratio

• Lamellae have:

  • A good blood supply

  • Are very thing

  • Maintain a good concentration gradient