Cellular Functioning - YR 11

Cell Membrane

Structure:

Double layer of lipid molecules and associated protein

Function:

Controls the movement of substances into and out of the cell

Cytoplasm

Structure:

Jelly like material inside the cell • Dissolved salts and carbohydrates • 75-90% water

Function:

Suspends the cell organelles • Controls osmotic pressure • Site of aerobic respiration

Nucleus

Structure:

Spherical in shape • Contains DNA enclosed in a double membrane (nuclear membrane) • Nuclear membrane contains pores through which molecules can pass

Function:

Controls the structure and functioning of the cell

Mitochondria

Structure:

Elongated in shape • Contains a double membrane (smooth outer and a folded inner membrane)

Function:

Release energy for the cell through the process of cellular respiration • Powerhouse of the cell

Ribosomes

Structure:

Very small and spherical • Free in cytoplasm or attached to the ER

Function:

Site of protein synthesis – amino acids are joined together here to form proteins

Rough Endoplasmic reticulum

Structure:

Complex network of channels formed by parallel membranes • Rough ER has ribosomes

Function:

Provides a surface on which chemical reactions can occur • Channels between the membranes are used for the storage and transport of materials • Rough ER is also a site for protein synthesis

Smooth Endoplasmic Reticulum

Structure:

Complex network of channels formed by parallel membranes • Smooth ER does not have ribosomes

Function:

Provides a surface on which chemical reactions can occur • Channels between the membranes are used for the storage and transport of materials

Golgi Body

Structure:

Flattened membranes stacked on top of each other

Function:

Modify and package proteins into vesicles for secretion from the cell

Vesicle

Structure:

Liquid enclosed by lipid bilayer (membrane)

Function:

Used in the process of secretion (exocytosis), uptake (endocytosis) and the transport of material within the cell.

Lysosomes

Structure:

Small spheres that contain digestive enzymes • Membrane bound • Formed by Golgi body

Function:

Fuse with particles taken into the cell to break it down. • Breakdown worn out organelles

Centrioles

Structure:

Pair of cylindrical structures at right angles

Function:

Involved in cell reproduction • Produces the spindle fibres needed to separate the chromosomes

Microvilli

Structure:

Tiny finger like projections on the surface of the cell • Non motile (does not move)

Function:

Assists with absorption and secretion • Increases the cell’ surface area

Cilia

Structure:

Projections of the cell membrane • Small, numerous projections • Larger that microvilli and motile

Function:

Cilia moves substances across the surface of the cell

Flagellum

Structure:

Long, few projections

Function:

Flagellum moves the whole cell

Functions of the cell membrane

Physical Barrier: Separates internal and external cellular environment allowing them to be different

Regulation of passage of materials: Controls movement of substances into and out of cell

Sensitivity: Receptors detect changes to external environment • Support: Attached to cytoskeleton supporting the whole cell

Fluid Mosaic Model

Fluid → the molecules of which the membrane is made change position/move • Mosaic → composed of many different molecules including phospholipids, proteins, carbohydrates and cholesterol

Cholesterol

Position:

In-between the phospholipid molecules

Function:

Maintains the fluidity of the membrane

Carbohydrate

Position:

Attached to proteins or phosphate heads on the exterior surface of the membrane

Function:

Act as markers to identify the cell and detect/recognise harmful cells

Protein – Channel - Position & Function

Position:

Embedded between the phospholipids - Span the lipid bilayer

Function:

Channel – Transport ions

Protein - Carrier - Position & Function

Position:

Embedded between the phospholipids - Span the lipid bilayer

Function

Carrier – Transport molecules

Protein- Receptor - Position & Function

Position:

Embedded between the phospholipids Span the lipid bilayer

Function:

Communication with external environment/detection of harm

Selective Permeability

Membrane that permits the passage of certain substances but restricts the passage of others.

Intracellular fluid

The fluid contained within a cell

Extracellular fluid

Fluid found outside of cells. Includes the blood/plasma and the fluid found in between cells, the interstitial fluid

Active Transport

Transports materials across the cell membrane from an area of low concentration of a substance to an area of high concentration of a substance/ against the concentration gradient - requires energy

Passive Transport

Transports materials across the cell membrane from an area of high concentration of a substance to an area of low concentration of a substance/ with the concentration gradient - doesn’t require energy

Concentration gradient

A concentration gradient occurs when the concentration of particles is higher in one area than another.

Diffusion

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

Process of Simple Diffusion

The process of substances in a solution, moving from an area of high concentration to an area of low concentration in solution across a semi-permeable membrane, through the lipid bilayer, without the use of energy and membrane proteins

Substances that can cross through the cell membrane through simple diffusion

Small, uncharged molecules such as oxygen and carbon dioxide and lipid soluble substances like alcohol, steroids and fatty acids

Osmotic Pressure

The pressure required to prevent the inward flow of water. The higher the concentration of the solute on one side of the membrane the higher the osmotic pressure. The higher the pressure, the more likely water will diffuse in.

Osmosis

The diffusion of water molecules across a semi-permeable membrane from an area of higher water concentration/lower solute concentration to an area of lower water concentration/higher solute concentration

Hypotonic

• There is a dilute solution

• Solute concentration outside is lower than inside the cell.

• Water moves into the cell

• The cell may become swollen and may rupture

Isotonic

• Normal solution

• Solute concentration outside is the same as inside the cell.

• There is no net movement of water

• No change in the shape of cells

Hypertonic

• There is a concentrated solution

• Solute concentration outside is higher than inside the cell.

• Water moves out of the cell

• This causes the cells shrink and crinkle (crenation)

Chanel Protein - Facilitated Diffusion

• Substances are transported through the protein channel from an area of high concentration to an area of low concentration, without the input of energy.

• Substances move through a central pore

• Hydrophilic charged particles like WATER AND IONS

Carrier Protein - Facilitated Diffusion

1. Substance binds to the binding site of the carrier protein

2. The protein changes shape and opens to the other side 3.The molecule is released.

3. Substances move by the carrier protein from an area of high concentration to an area of low concentration, without the input of energy.

• Large molecules Hydrophobic molecules like GLUCOSE AND AMINO ACIDS

Characteristics of Carrier Mediated Proteins

• Are specific : they will only bind to a specific molecule.

• Can become saturated : once all carriers are occupied, any increase in the concentration of molecules to be transported cannot increase the rate of movement.

• Are regulated by hormones : Hormones regulate the functioning of carrier proteins

Carrier Mediated Active Transport

• The movement of large molecules/ through a carrier protein from an area of low concentration to an area of high concentration with the use of energy.

  1. Substance binds to the binding site of the carrier protein

  2. The protein changes shape and opens to the other side

  3. The molecule is released.

  4. Molecule detaches from the protein

  5. Protein reverts to its original shape

• Glucose, amino acids and certain ions (sodium and potassium)

Vesicular transport

The movement of molecules into or out of the cell in a vesicle

Endocytosis - Definition

Movement of substances into the cell via a vesicle

Exocytosis - Definition

Movement of substances out of the cell via a vesicle

Phagocytosis

Movement of solids

Pinocytosis

Movement of liquids

Endocytosis

• The cell membrane folds around the particles until it is completely enclosed. The vesicle formed pinches off and is suspended within the cytoplasm.

Ex.

• Phagocytosis → Bacteria cells

• Pinocytosis → Hormones/cholesterol

Exocytosis

• A vesicle that is formed inside the cell migrates to the cell membrane and fuses with the membrane. The contents of the vesicle are then pushed out into the extracellular fluid

Ex

• Digestive enzymes and mucous

Four types of substances that are secreted from cells.

Hormones

Enzymes

Hydrochloric acid (in the stomach)

Mucus

5 Factors Affecting Rate of Transport

1. Surface Area to Volume Ratio

2. Concentration Gradient :

   • The greater the difference in concentration of a substance between sides of the cell membrane (the greater the concentration gradient) the faster the rate of diffusion

3. Type of molecule

   • Fast = small, uncharged, lipid soluble = easily pass through the cell membrane

   • Small = large, charged, water soluble =

   • These molecules need a transport protein to be transported

4. Distance

5. Temperature

Metabolism

The sum of all chemical reactions that take place within a cell

Catabolic

• Large molecules are broken down into smaller molecules, releasing energy

• Releases energy

Ex.

Cellular respiration

Digestion

Anabolic

• Small molecules are built up into large molecules with the use of energy

• Uses energy

Ex.

Protein synthesis

DNA replication

Cellular Respiration

Is a series of chemical reactions by which chemical energy stored in glucose is released as ATP – a molecule of energy the cell can use.

ATP process

• ADP and phosphate molecules are freely floating in the cytoplasm

• Energy is produced during cell respiration

• This energy is used to join a phosphate molecule onto an ADP molecule to make ATP.

• Energy is stored in the bond between the 2nd and 3rd phosphate groups

• When energy is required by the cell, this bond is broken, releasing energy and the 3rd phosphate

• Energy is used by the cell, and we are left with ADP + phosphate

• ATP is a renewable resource. It can be broken down to form ADP + P + energy for use by the cell, or converted back in to ATP for energy storage.

Aerobic Respiration

Breakdown of glucose in the presence of oxygen to yield 38 molecules of ATP, carbon dioxide and water.

Glucose + oxygen → + water + carbon dioxide + energy (38 ATP)

Process of Aerobic Respiration

Step 1: Glycolysis :

• Occurs in the cyctoplasm

• Oxygen is not required

• A glucose molecule is broken down into 2 molecules of pyruvate and 2 molecules of ATP.

Step 2: Citric acid cycle & the electron transport system

• Occurs in the mitochondria

• Oxygen is required

• Both pyruvate molecules enter mitochondria. The two pyruvate molecules are converted into carbon dioxide. Formation of 2 more ATP molecules (1 per pyruvate. Remaining components of pyruvate broken down.

Anaerobic Respiration

Breakdown of glucose in the absence of oxygen to yield 2 molecules of ATP and lactic acid

Glucose → energy (2 ATP and heat) + lactic acid

Process of Anaerobic Respiratoin

Step 1. Glycolysis

• Occurs in the cyctoplasm

• Oxygen is not required

• A glucose molecule is broken down into 2 molecules of pyruvic acid and 2 molecules of ATP.

Step 2. Fermentation

• Occurs in the cytoplasm

• Oxygen is not required

• The two pyruvate molecules are converted into lactic acid

• Lactic acid is transported to the liver where it reacts with oxygen to form glucose.

Cells

The basic structure and functional units of an organism Cells are specialised to carry out specific functions

Tissues

Groups of cells with related functions form tissues

Organs

Differentiated tissue types group together to form an organ which carries out a specific function

System

Groups of organs with a common function form a system

Organism

The cooperation of all systems makes up an organism

Epithelial Tissue

Function:

Protects underlying structures from wear, infection or pressure. Cells may be specialised for absorption, secretion or excretion.

Location:

Lines external and internal surfaces of the body eg skin, lining of the respiratory and digestive tract.

Structure:

Simple (single layer) or stratified (multiple layers) It can be ciliated

Nervous Tissue

Function:

To carry messages/impulses around the body

Location:

Brain, spinal cord and nerves

Structure:

Consist of a cell body with a long extension called an axon

Connective Tissue

Function:

To provide support for the body and to help hold the body parts together

Location:

Under the skin, cartilage, blood, bone, ligaments, tendons and adipose tissue/fat

Structure:

Cells are scattered through a matrix

Cardiac Muscular Tissue

Function:

• To produce the heartbeat

Location:

• Heart

Structure:

• Consists of elongated cells

• Striations

• Branches

Control:

• Involuntary

Smooth muscular tissue

Function:

• Produce movement of internal structures

Location:

• Digestive organs and blood vessels

Structure:

• Consists of elongated cells

• No striations

• No branches

Control:

• Voluntary

Skeletal Muscular Tissue

Function:

• Produce movement of the body for locomotion

Location:

• Skeletal muscles attached to bones

Structure:

• Consists of elongated cells

• Striations

• No branches

Control:

• Involuntary