Exchange Across the Membrane
- Active transport:
- Against a concentration gradient via carrier proteins that use energy from ATP in order to change shape.
- Endocytosis and Exocytosis:
- Bulk transport of materials via vesicles that can fuse with or break from the cell surface membrane.
- Down a concentration gradient lipid soluble or very small molecules throught lipid bilayer and osmosis..
- Facilitated Diffusion:
- Down a concentration gradient charged or hydrophilic molecules or ions via channel or carrier protiens.
- Diffusion is a passive process.ie. molecules diffuse down gradient with not energy needed, they have their own kinetic energy.
- The rate is affected by
- Concentration gradient
- Surface area
- Size of molecule
- Channel Proteins:
- Are like pores, only allow one type of ion through sometimes are gated. Ions like Na ions and Ca ions
- Carrier Proteins:
- shaped for specific molecule, protien changes shape to allow mollecule through eg. Glucose and amino acids.
Water Potential/ Osmosis
- is a special kind of diffusion, it is only the movement of water molecules by diffusion and across a partially permeable membrane.
- Water potential is a measure of the concentation of water molecules that are able to diffuse. Pure water has the highest amount of free molecules 0kPA (kiloPascals). Lower water potential is -10kPA.
- In Pure Water
- Animal cells take in water from osmosis until they burst open (haemolysed)
- Plant Cells have a cell wall which prevents bursting. Membrane pushes against the wall (Turgid).
- In Concentrated solution
- Animal cell loses water through osmosis and shrinks and appears wrinkled (Crenated).
- Plant cell loses water through osmosis and plant cell membrane pulls away from cell wall as water leaves. (Plasmolysed)
Mitosis is significant in a cell because it is involved with:
- Growth .e.g. cells in an eymbryo divide to form tissue stem cells
- Replacement of cells.eg. Bome marrow to Red blood cells and neutrophils.
- Repair, e.g. in wound healing.
- Asexual reproduction
The Stages of mitosis:
- Prophase - replicated chromosomes supercoil (shorten and thicken),each chromosome is now two chromatids.Nuclear envelope breaks down. Centrioles move to opposite poles of the cell.
- Metaphase - Chromatids come to the middle of the cell. Centrioles organise microtubules into the spindle which attach to centromes.
- Anaphase - Chromatids break apart at the centromere and are pulled by the spindle towards poles. Once separated they become chromosomes.
- Telophase - Nuclear envelopes re-form around each group of chromosomes at each end of the cell. The chromosomes uncoil.
Cell division and mitosis
The cell cycle is divided into stages:
- Interphase - DNA replicates in this stage.
- mitosis - the nucleus divides and chromatids separate.
- cytokinesis - the cytoplasm divides or cleaves.
- Growth phase - each new cell grows to full size.
Mitosis is involved in :
- Growth eg. cells in an embryo divide to form tissue stem cells
- Replacement of cells, e.g. tissue stem cells in bone marrow divide to produce red blood cells and neutrophils.
- Repair, e.g. in wound healing
- asexual reproduction
Mitosis in four stages
Mitosis in four stages:
- Replicated chromosomes supercoil (shorten and thicken), each chromosome has two chromatids. The nuclear envelope begins to break up. Centrioles move to opposite ends of the cell to make the poles.
- Chromosomes line up down the middle of the cell (equator). Centrioles organis microtubules into the spindle that straches across the cell. Chromosomes are attached to the spindle at the centromere.
- Chromatids break apart at the centromere and are pulled by the spindle towards the poles. Once separated, the chomatids are chromosomes.
- Nuclear envelopes re-form around each group of chromosomes at either end of the cell. The chromosomes uncoil.
Cell cycle and life cycles are not the same
- Stem cell - Undifferentiated cells that are capable of becoming differentiated to a number of possible cell types.
- Homologous pair of chromosomes - chromosomes that have the genes at the same loci. Members of an homologous pair of chromosomes pair up during meiosis.
- Budding - nucleus divides first, followed by the cytoplasm
- Adult human carries out meiosis only in (specialised regions) sex organs to prodice gametes.
- Meiosis produces cells in humans containing 23 chromosomes
- Egg and sperm fuse to form a zygote with 46 chromosomes in humans
- Repeated mitosis from zygote results in a adult.
- have no nucleus, mitochondria, Golgi apparatus and rough ER.
- are packed full of haemoglobin
- shape changes so they become biconcave disces and they are then capable of transporting oxygen from lungs to tissues.
- keep their nucleus
- cytoplasm appears granular because enormous number of lysosomes produced.
- ingest invading microorganisms - so potent enzymes in lysosomes enable the neutrophils to be specialised for killing microorganisms.
Organising the organism
- A collection of cells that are similar to each other and perform a common function. They may be found attached to each other, but not always. eg. xylem and phloem in plants.
- A collection of tissues working together to perform a particular function is called an organ. eg. leaves in plants and the liver in animals.
- An organ system is made up of a number of organs working together to perform an overall life function. eg. excretory system and the reproductive system.
Plant tissues :
- Xylem and phloem come from diving meristem cells such as cambium.
- Meristem cells undergo differentation to form the different kinds of cells in the transport tissues.
- Xylem transports water and ions.
- Phloem transports sugars (mainly sucrose) and other compounds made by plants.
- Squamous epithelial tissue:
- made of flattened cells, thin, smooth, flat surface. Ideal for lining inside of tube ie. blood vessels, Where fluids can pass easily over them.
- are held in place by the basement membrane, it is made out of collagen and glycoprotiens.
- Ciliated epithelial tissue:
- made up of column-shaped cells
- found on the inner surface of the tubes eg. trachea, bronchi and bronchioles.
- "exposed" surface covered with tiny projections called cilia, which wave in rhythm and move stuff like mucus.