Biology - Unit 1

Nucleus:

Description: Large, normally spherical struture containing thread-like chromosomes

Function: Conntrols cell activitites and passses info on from cell to cell

Cytoplasm:

Description:  Jelly-like substance that makes up most of the cell

Function: Site of reactions 

Cell Membrane: 

Description: Thin layer surrounding cytoplasm 

Function: Controls passage of substances into and out of the cell

Cell Wall:

Description: Outer layer made of basket-like mesh of fibres

Function: Supports the cell

Large Vacuole:

description: Fluid-filled sac-like structure on cytoplasm 

Function: Stores water and solutes as cell sap and regulates water content

Chloroplasts:

Description: One of many discus-shaped structures containing green chloroplasts

Function: PHOTOSYNTHESIS 

Notes:

• A double layer of phospholipids molecules (phospholipid bilayer) is held togther by weak internal forces which allow individual molecules to move.
• In the phospholipid bilayer is collage of protein molecules.
•  These protens can be found in either layer or spannng both layers of the membrane.
• Cell organelles are thought to have membranes with this same structure.
• The proteins molecules in the membrane can have a variety of functions:
• They allow water, glucose, amino acids, ions and other small molecules to pass though the membrane into and out of the cell - through the pores between the cahnnel. proteins.
• Some actively pump molecules across the membrane - this is active transport and requires energy.
• They are receptors for antibodies or for hormones
• They are proteins that provide structure for the membrane (Structural proteins)
• They are enzymes

Notes:

• Molecules are too big to pass through the pores are kept in or out of the cell.
• For this reason the cell membrane is said to be selectively permable
• The cells membrane is freely permable to samll molecules like oxygen, carbon dioxide and water.
• They can cross the membrane quickly.
• Larger molecules of dissolved (soluble) food e.g glucose cross the membrane slowly.
• Very large molecules, like strach cannot cross the cell membrane.

Notes:

• Particles moving from a high concentration to a low concentration
• Described as moving down a concentration gradient
• The difference in concentration that exists between two regions beofre diffusion occurs is called the concentration gradient 
• During diffusions molecules alwasy move down a concentration gradient from high to low
• The bigger the differnce bwtween the 2 concentrations the faster the diffusion occurs
• Diffusion is a passive process (This means that the process doesnt require energy)
• Diffusion is important to living cells since it provides a way by which useful subsatnces e.g oxygen and food, enter the cell and the waste products e.g carbon dioxide leave the cell.
• Cells take in (uptake) oxygen by diffusion.  This means that oxygen moves from a high concentration outside the cell to a low concentration inside the cell.

Notes:

• The water concentration of an animals blood changes according to how much water the animal drinks, what the animal eats nad how much water the animal loses in sweat.
• The animals body has systems to maintain as constant a water concentration as possible so that cells work effciently as possible.

In an normal cell (water in = water out)

• Cytoplasm pushes against cell wall
• Cell wall slightly swollen 
• The cell is described as partically turgid (solid)

In an hypotonic cell (water in to cell)

• Vacuole slightly against cell wall
• Cytoplasm pushed against cell wall
• Cell wall extended to maximum
• The cell is described as being fully turgid (very solid and hard)

In an hyperonic cell (water out of cell)

• Vacuole shrunken 
• Cytoplasm pulled away from cell 
• Cell wall is unstreched 
• This process of extreme water loss is called plasmolysis

Notes:

•  Active transport is the movement of ions and molecules through the cell membrane from a lower concentration of the ions/molecules to a higher concentration of the ions/molcules, against the concentration gradient.
• This process uses protein carrier molcules in the membrane to transfer specific ions/molcules across the cell membrane
• Thsi requires energy.

• The nucleus carries the genetic information called chromosomes.
• A gene is a length of DNA which codes for a charcteristic
• Nucleotides have three parts: suger molcules, phosphate molecule and a base molecule.
• Only the bases are different
• DNA bases: Adenine, Thymine, Guanine and Cytosine.  A and T are together and G and C are together.
• Held together by weak hydrogen bonds.
• A protein molecule is made up from amino acids bonded by peptide bonds.
• The genes (for making the proteins) are in the nucleus but the ribosomes (where proteins are made) are in the cytoplasm.  This means the information to make a protein must be carried from the DNA in the nucleus to the ribosomes in the cytoplasm.  This is done by a molecule called messager RNA (mRNA).
• Messager RNA copies the code from the DNA and then travels out of the Nucleus into the cytoplasm where the mRNA attaches to a ribosomes.  Amino acids arrives at the ribosomes form peptide bonds with the next amino acids arriving at the ribosome accroding to the sequence of bases on the mRNA.

• The variety of proteins shapes and function depends on the sequence of amino acids that make them up.
• Proteins have many functions: structural enzymes, hormones, antibodies and receptors.
• The shape of the active site of an enzyme molecule is complementary to its specific substrates
• Enzymes can be involved with degradation reactiosn nad synthesis reactions.

• Genetic information in the form of DNA can be transferred from one cell to another naturally.
• Bacteria can also pass DNA to other bacteria, plant and animal cells naturally.
• The part of the gene is inserted into plasmid then inserted into bacterium.
• Called generic modified organism.

• Respiration is the energy stored in glucose must be released by all cells through a series of enzymes controlled reactions.
• The energy released from the breakdown of glucose is used to generate ATP.
  
• The energy transferred by ATP can be used for cellular activities.
• Glucose is broken down into two molecules of pyruvate, releasing enough energy to yield two molecules of ATP#
• Further breakdown depends upon the presence/absence of oxygen 
  
• if oxygen is present, aerobic respiration will take place and place pyruvate is broken down to carbon dioxide and water, releasing enough energy to yield a large number of ATP molecules.
  
• If oxygen is absence the fermentation pathway takes place.  In animal cells, pyruvate molecules are converted to lactate and in plant and yeast cells, they are converted to carbon dioxide and ethanol.  The breakdown of each glucose molecule via the fermentation pathway yields only the initial two ATP molecules.
  
• Respiration begins in the cytoplasm.  The process of fermentation is complete in the cytoplasm whereas aerobic respiration in completed in the mitochondria.