Structure and Function of Cells Chapter 2

Looking at cells Living cells can be classified into 2 different kinds: Prokaryotic cells Eukaryotic cells All cells have an outer boundary known as the plasma membrane (or cell membrane)

Prokaryotic cells have very little defined internal structures. They are very simple cells. This includes bacteria Eukaryotic cells are much more complex. They contain membrane bound organelles. Organelles are structures that perform the tasks that a cell needs to do. This includes all animals, plants, fungi, other single celled organisms

The plasma membrane boundary Controls entry and exit of substances Is very thin (0.01µm) Present in prokaryotes and eukaryotes Is ‘partially permeable’ meaning it is selective about which dissolved substances are allowed in or out.

Consists of a ‘phospholipid bilayer’ ‘Fluid mosaic’ model describes the form it takes

Free passage: Diffusion Diffusion is the net movement of a substance from a region of high concentration to a region of low concentration. It is a passive process (does not require energy) See simulation on scootle

Osmosis: a special case of diffusion Osmosis is the movement of water from an area of low solute concentration (high in water, low in dissolved substances) to an area of high solute concentration (low in water, high in dissolved substances) UNTIL the concentration is equal See simulation on scootle

Facilitated diffusion In some cases, movement of substances across the membrane is assisted by carrier protein molecules (think back to the ‘fluid mosaic’ model) This occurs when the substances are unable to move through the lipid bilayer. It is a passive process (does not require energy) hill.com/sites/ /student_view0/chapter2/anim ation__how_facilitated_diffusion_works.html hill.com/sites/ /student_view0/chapter2/anim ation__how_facilitated_diffusion_works.html

Paid passage: active transport Active transport is the movement of dissolved substances against a concentration gradient (the OPPOSITE of diffusion) It is an energy requiring process hill.com/sites/ /student_view0/chapter2/anim ation__how_the_sodium_potassium_pump_works.html hill.com/sites/ /student_view0/chapter2/anim ation__how_the_sodium_potassium_pump_works.html

Bulk transport Endocytosis and exocytosis are two methods for moving large particles into and out of cells. Endocytosis involves the cell membrane ‘engulfing’ a foreign object and moving it into the cytosol. Eg white blood cells Exocytosis involves a vesicle (containing whatever is to be released) fusing with the cell membrane and release its contents into the environment surrounding the cell See figure 2.12 pg 30 Phagocytosis: solid material Pinocytosis: fluid material

Surface area to Volume ratio SA:V Cells are small Some cells have folded membranes Cells must maintain a favourable SA:V which means that their surface area is sufficient to take up materials essential for cell functioning. Refer to biozone activity- pg 79 See pg 44 of text

Cell walls Not found in ANIMAL cells In plants, fungi & bacteria, a cell wall exists outside the plasma membrane Cell walls provide organisms with a rigid support structure

Cell organelles The nucleus: control centre Mitochondrion: energy supplying organelle Nuclei are present in eukaryotic cells The nucleus contains the genetic material (DNA) of the cell, which provides ‘instructions’ for performing all of the tasks that a cell needs to do. Mitochondria complete cellular respiration in order to provide ATP for cellular activities. They are the ‘powerhouse’ of the cell

Cell Organelles (cont) Ribosomes: protein factories Lysosomes: controlled destruction Ribosomes makes proteins for use in the cell or for export outside the cell (eg hormones) Programmed cell death: apoptosis Lysosomes contain digestive enzymes, which can be released to cause the ‘self destruction’ of the cell

Transport, storage and export Endoplasmic reticulumGolgi complex Transports proteins within the cell. Can be called ‘rough ER’ or ‘smooth ER’ Rough ER is surrounded by ribosomes. Transports substances made in the cell to outside the cell

Chloroplasts Flagella & cilia: whipping around. Found in PLANT cells only Site of photosynthesis: the trapping of sunlight and conversion to chemical energy in the form of glucose. Contain the substance chlorophyll, a green, light trapping pigment Are found in cells where movement is required. Flagella are a ‘tail’ structure, where its movement cause the cell to move. Cilia are hair like structures- movement of cilia may cause the cell to move, or may cause things outside the cell to move past it. (Eg trachea)

Cells in multicellular organisms: levels of organisation Cells  tissues  organs  systems

Homework Biozone pgs 73, 75,76-77, 81, 83 Plant and animal cells pgs Practical report from last weeks prac