Osmosis

• Definition: The net movement of water molecules across a semipermeable membrane (things can pass through) from an area of low solute concentration (dilute solution) to an area of high solute concentration (concentrated solution), down the water concentration gradient.

• a passive process (doesn’t need energy from respiration)

Types of Solutions

• Hypotonic Solution

  • Water moves into the cell causing it to swell or burst.

  • Less solute than solvent

  • Soluton that is less concentrated than that in the cell

• Hypertonic Solution

  • Water moves out of the cell causing it to shrink or shrivel.

  • More solute than solvent

  • Solution that is more concentrated than that in the cell

• Isotonic Solution

  • Water moves equally in and out of the cell, maintaining equilibrium, net movement = 0.

  • The solute and solvent are equal

  • Water concentration is the same inside and outside the cell

Factors Affecting Osmosis

• Concentration Gradient

  • The difference in solute concentration between two areas.

  • The larger the concentration gradient, the faster osmosis occurs

• Temperature

  • Higher temperatures increase the rate of osmosis, as kinetic energy increases.

• SA:V Ratio

  • higher the ratio, more points of entry or exit, faster osmosis

• Permeability of the Membrane

  • more permeable, faster osmosis

Biological Significance

• Cellular Processes

  • Osmosis is crucial for processes like nutrient uptake and waste removal in cells.

• Plant Cells

  • Osmosis helps in maintaining turgid pressure in plant cells.

• Kidney Function

  • Osmosis plays a role in the filtration of blood in the kidneys.

• the net movement of water is from a hypo - hyper tonic solution

• turgid - cell swells, cell membrane pushed against cell wall and cell

• flaccid - water has left the cell and the cell membrane isnt pushing against the cell wall

• plasmolysed - water has left the cell and the cell membrane has shrunk away from the cell wall

• lysis - when a cell swells and burst

• crenation/crenated - when a cell shrivels up

• haemolysis - when red blood cells burst

Diffusion

• Diffusion: The net movement of particles from an area of high concentration to an area of low concentration.

• Factors Affecting Diffusion

  • Concentration Gradient

  • Temperature

  • Surface Area

  • Distance

• Examples of Diffusion

  • Gas Exchange in Lungs

  • Nutrient Absorption in Intestines

  • Water Uptake in Plants

• Exchange Surfaces

  • roots

  • fish gills

  • villi

  • leaves

  • lungs

  • placenta

• How organisms are specialised for exchanging materials

  • Large SA

  • Thin membrane/walls for exchanging materials

  • Efficient blood supply

  • Ventilation

Active Transport

• the movement of a substance against a concentration gradient (low to high concentration), using energy from cellular respiration

• Requirements

• Carrier Proteins

  • pump substances across the membrane

• Energy (from ATP)

  • molecule produced by cellular respiration in the mitochondria

• active transport is an active process (requires energy)

• It is always across the membrane

Plant and Animal Cells

• animal cells have DNA/genetic material, cell membrane, nucleus, cytoplasm, mitochondria, and a golgi body/apparatus

• plant cells contain the above, plus a cell wall made of cellulose, ribosomes, and a vacuole

• fungal cells like yeast contain DNA, nucleus, ribosomes, cell wall, cell membrane, cytoplasm, vacuole, and mitochondria

• bacteria cells contain ribosomes, cell wall, cell membrane, slime capsule, enzymes, cytoplasm, flagellum, pili, freefloating DNA/nucleoid, and plasmids

Functions of Organelles

• Nucleus

  • controls the cells activities, and contains necessary genes for chromosomes to function, and DNA, which is genetic material

• cytoplasm

  • liquid gel in which chemical reactions take place

• cell membrane

  • controls what enters and exits the cell

• mitochondria

  • site of respiration, and releases energy in the form of ATP for the cell

• ribosomes

  • site of protein synthesis

  • organises amino acids into a sequence determined by the DNA

• chloroplasts

  • contains chlorophyll which absorbs sunlight for photosynthesis

• vacuole

  • sack that contains all disolved sugars and waste

  • exerts pressure on the cell wall

  • filled with cell sap

• cell wall

  • maintains cell shape and provides structural support

  • prevents pathogens from entering

• golgi apparatus/body

  • modifies and packages proteins and some fats

Cell Specialisation

nerve cells

• lots of dendrites to make connections to other nerve cells

• a long aton that carries the nerve impulses from place to place

• endings are adapted to pass impulses using special transmitter chemicals

• specialised to carry electrical impulses around the body

muscle cells

• contain special proteins which enable it to contract and relax (fibres)

• many mitochondria for energy

• myoglobin to store energy for respiration

sperm cells

• streamline head for faster swim spead

• tail to aid swimming

• lots of mitochondria for energy to swim

• energy stored in head to help break the egg

• delivers DNA to the egg and fertilises it, turning it into a zygote

root hair cells

• increased SA for water to move into the cell

• large vacuole speeds up movement of water

• many mitochondria for energy needed for active transport of mineral ions

• allows plants to absorb more water

red blood cells

• biconcave disk for increased SA

• haemoglobin to enable it to carry more oxygen

• no nucleus or other organelles to fit more haemoglobin

• carries oxygen from lungs and delivers it throughout the body

xylem cells

• lignin chemical builds up to allow water and minerals move through easily

• spirals and rings support the pressure

• to carry water and mineral ions from the roots to the highest leaves and shoots and support the plant

phloem cells

• cell walls break down to let dissolved food move more freely

• mitochondria in companion cells transfer necesary energy

Cell Differentiation

• as an organism develops, cells differentiate to form different types of cells

• most animal cells differentiate early

• as a cell differentiates, it acquires different sub-cellular structures that enable it to carry out it’s function

Microscopy

• electron microsopes can view up to 1000x better magnification than light light microscopes, but are very expensive

• magnification: degree to which the size of an image is larger than the object itself

• to calculate magnification:

  • multiply magnification eyepiece lense by objective lens

  • eg. x4 * x10

  • = 4×10

  • = x40

• magnification = size of image / size of real object

  

Culturing Microorganisms

Binary Fission - bacteria can replace approx. every 20mins through Binary Fission, a simple form of cell division

example: A bacteria cell has a mean division time of 30mins. How many cells would it produce after 3 hours?

Required Practical 6

METHOD

1. sterilise agar and petri dish in an autoclave to kill bacteria

2. turn on the bunsen burner on a roaring flame, and place the agar plate facing the air hole

3. sterilise the inoculating loop in the flame

4. collect the microbes using the inoculating loop

5. hold the lid at 45 degree angle and streak the agar surface

6. repeat steps 3-5 multiple times

7. place lid and secure with 4 pieces of tape, to allow oxygen for respiration

8. place petri dish upside down to prevent condensation dripping onto the agar

9. place the inoculating loop in Virkam to be cleaned

10. when rested and viewed, kill bacteria in an incubator at 28-30 degrees celsius to prevent pathogens from growing

    *an inoculating loop is also called a nicrome wire

autoclave - strong heated container used to sterilise equipment

incubator - used to grow or maintain cultures at a set temperature

sterile - no microorganisms present

inoculation - adding microorganisms to something, like being vaccinated

culture - growth of bacteria, like a colony

aseptic - only growing an organism

Chromosomes

• strips of DNA which have been tightly coiled

• each cell contains 23 pairs of chromosomes

• in each pair, one from the mother and one from the father

karyotype - organised computer generate display of the pairs of chromosomes as seen through a microscope

Bases

• adenine bonds to thymine

• cytosine bonds to guamine

Genes

• small section of DNA or a chromosome

• codes for a particular sequence of amino acids to make a protein

• in the last chromosome:

  

Mitosis and the Cell Cycle

Stage 1 - Interphase/Resting Phase

• longest phase

• cell does its usual day to day functions

• elongates, multiplying its sub cellular structures, and gets bigger

• copies all of its DNA towards the ends which forms 2 copies of each chromosome ready for cell division

Stage 2 - Mitosis

• nucleus divides, and one set of chromosomes is pulled to each side of the cell

• 4 sub stages - prophase, metaphase, anaphase, and telophase

Stage 3 - Cytokinesis

• cell membrane and cytoplasm divide to form 2 identical daughter cells

• most cells can keep going through the cycle, but some cant

• if the DNA doesnt copy over correctly, Mutation, it can cause cancer or the cell will be killed

Cell enlargement (during interphase)

• no. of organelles will increase

• cytoplasm volume increases

• chromosomes will split then keep on doubling

• chromosomes line up on an equater, sister chromatids are pulled to opposite sides, the nucleus membrane forms around each set of chromosomes, then cytokinesis occurs

• mitosis helps us grow bigger or repair

• it produces sex cells/gametes

• teeth, skin and muscle are made through mitosis

• almost always, cell division is mitosis

• most of a cells life is in interphase

• mitosis takes place for cell renewal, tissue repair, growth, and asexual reproduction

• the cell cycle can take less than 24 hours, or several years, depending on the cells involved and the stage of life of the organism

• the cell cycle is fast when young, and slows down after puberty

• parent and daughter cells are genetically identical

Stem Cells

TOTIPOTENT

• have the ability to divide and produce all the differentiated cells in an organism

• includes non body tissue like the umbilical cord and placenta of the foetus

PLURIPOTENT

• ability to divide all the types of body cells, but not umbilical cord or placenta

MULTIPOTENT

• also called adult stem cells

• can differentiate into a limited no. of body cells, usually the cells of one organ

• permanently committed to a specific function