C E L L S

Plasma Membrane Extensions

Plasma membrane Extensions increase the surface area of the cell membrane without increasing the volume of the cell. This is done differently in different cells however often it is increased through small hairs or finger-like extensions attached to the plasma membrane. Example: Some animal cells have microvilli and some plants have root hairs which allow the plant absorb more water and nutrients from the soil, also the small intestine has larger finer like projections called villi.

Plasmolysis

Plasmolysis occurs when plant cells are placed in a hypotonic environment and water is drawn out of the cells. When this happens the large vacuole shrinks and the cell membrane pulls away from the cell wall causing inside of the cell to shrink while the cell wall still remains rigid.

Plant and Animal Cell Difference

- Cell wall which adds support in plant cells - Larger vacuole - provide support by maintaining tugor structure

Benefits of Compartmentalisation

- It allows enzymes and reactants for a particular function to be close together in high concentrations and at the right conditions so that processes within the organelles are very efficient - It allows processes that require different environment to occur at the same time, the same cell. - It makes the cell less vulnerable to changes to its external environment, because changes will affect the cytosol much more than the membrane-bound organelles.

Similarities between plant and animal cells

- Nucleus - Cytoplasm - Plasma membrane - Mitochondria - Endoplasmic reticulum - Golgi apparatus

Hypertonic

A cell is said to be in a hypertonic solution when the concentration of solutes is higher outside the cell than inside. In a hypertonic solution the water will be drawn out of the cell to an area higher solute concentration and the cell will shrink or undergo plasmolysis depending on the cell type.

Hypotonic

A cell is said to be in a hypotonic when the concentration of solutes is lower outside the cell than inside. In a hypotonic solution water will be drawn into the cell to an area of higher solute concentration and the cell will expand and may burst or become turgid depending on the type of cell it is.

Isotonic

A cell is said to be in an isotonic solution when the concentration of solutes is the same inside the cell as it is outside the cell. In an isotonic solution water will move in and out of the cell at the same rate

Cilia

A cilium is an organelle found in eukaryotic cells. It is a minute hair-like organelles, that lines the surfaces of certain cells and beats in rhythmic waves. It consist of an arrangement of micro tubes enclosed by an extension of the cell membrane. Cilia and flagella have the same structures but different beating patterns. Example: In mammals the cells lining the air passage have cilia to aid in the movement of mucus and dirt out of the lungs.

Concentration Gradient

A concentration gradient occurs when there is a difference in the concentration of a solute between one region and another (such as across a membrane).

Osmotic Gradient

A difference in concentration of a solute (dissolved substance) on each side of a semi-permeable membrane.

Flagella

A flagellum is a whip-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells. The primary role of the flagellum is locomotion.The flagellum is rotated to create movement of the cell. Some cells have more than one flagella. The flagella is made of an arrangement of micro tubes enclosed by an extension of the cell membrane. Flagella and cilia have the same structure but different beating patterns. In mammal, sperm cells have a flagella.

A Flattened Shape

A flattened shape means that there is a larger surface area to volume ratio allowing a higher rate of exchange through the plasma membrane, and also reducing the distance that substances need to be transported to and from and plasma membrane. Example: Red blood cells

Lysosome

A lysosome is a membrane bound organelles found in most animal cells. Lysosomes are small vesicles containing digestive enzymes responsible for breaking down large molecules and unwanted structures in the cell. The do this by fusing with vesicles containing unwanted matter such as damaged organelles or foreign matter and then digesting the matter through the enzymes in lysosomes. In this way they act as the waste disposal system of the cell. Lysosomes can also release enzymes into the cell for 'programmed cell death'. Lysosomes are not found in prokaryotes and are potentially found in plant cells.

Enzymes

A protein molecule that catalyses biochemical reactions

Vesicle

A small organelle consisting of a membrane filled with fluid. Vesicles are often involved in transport within the cell, but may have other functions.

Cell membrane-barrier

Cell membranes separate: the inside of the cell from the outside, one cell from another and different compartments within the cell from each other.

Active Transport

Active Transport is the movement of particles from a region of low concentration to a region of high concentration. This type of transport requires energy and also requires a protein carrier to transport particles against or up their concentration gradient.

General Cells

All cells have 4 common features: A plasma membrane, cytoplasm, DNA and ribosomes

Animal Cells

Animal cells are eukaryotic and are include the following organelles: the nucleus, mitochondria, Endoplasmic reticulum, Golgi apparatus, cell membrane, cytosol, DNA and ribosomes

Organelles

Any specialised structure in the cytoplasm of a cell, including the Golgi apparatus, mitochondria, endoplasmic reticulum, vacuole, chloroplast and nucleus. Organelles have different functions within the cell and require different internal conditions, including enzymes which catalyse the various reactions that occur there.

Carrier Protein

Carrier proteins are proteins that bind molecules (eg glucose) or ions on one side of the membrane and then change shape and release the molecules or ions on the other side of the membrane. Carrier proteins transfer these molecules or ions against the concentration gradient in a process known as active transport which requires energy.

Carrier proteins

Carrier proteins are transport proteins that change shape when molecules bind to them, so that the molecules can pass through the plasma membrane. Carrier proteins take part in facilitated diffusion and active transport.

Cell Compartmentalisation

Cell compartmentalisation allows eukaryotic cells to be much bigger than prokaryotic cells, because: - It reduces the amount of exchange that needs to occur across the plasma membrane to maintain an environment that is fit for all cell functions. - It creates more space for membrane bound enzymes, allowing increased activity in the cell.

Compartmentalisation

Cell compartmentalisation can occur in eukaryotic cells and is the formation in the cytosol of specialised structures enclosed by membranes, including the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, endosomes, lysosomes and chloroplasts. The membrane of these membrane bound organelles enable each organelle to have a different composition from the surrounding cytosol and other organelles.

Channel Proteins

Channel proteins are similar to tunnels that allow selected substances to pass through them from one side of the membrane to the other. Some channel proteins are open all of the time, continually allowing specific substances to pass through while others have 'gates' that usually block the flow unless they are triggered to open. Substances are able to pass through these channels through diffusion as it requires no energy.

Channel proteins

Channel proteins are transport proteins that molecules do not usually bind to. They function similar to pores that open and close and allow the passage of specific molecules. Channel proteins allow specific molecules to pass through the plasma membrane, and are used in facilitated and diffusion.

Chloroplasts

Chloroplasts are specialised organelles found in plant and algal cells but not in prokaryotes and animal cells. They are the organelle responsible for carrying out photosynthesis, the process by which light a transformed into chemical energy, to produce food in the form of sugars. Chloroplasts are green in colour due to the presence of the green pigment chlorophyll which captures the energy from sunlight . Chloroplasts also have an outer membrane and many stacks of chlorophyll-containing membranous stack called thylakoids, which increase the surface area for the capture of light to take place. The fluid between these stacks (grana) is called stroma.

Cholesterol

Cholesterol are fatty molecules which are found scattered in the lipid bilayer. The function of cholesterol is to keep the membrane fluid consistent in order to allow stability in the cell. They also reduce the permeability of the cell to small water soluble molecules.

Cytosol

Cytosol is a jelly-like liquid, that is made up of more than 80% water and contains ions, salts and organic molecules. This is the substance that the organelles are suspended in.

Endocytosis

Endocytosis is a type of vesicle transport that requires energy which refers to the movement of substances into a cell using vesicles. It is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. At this stage the membrane folds over the substance and it becomes completely enclosed by the membrane. Finally the membrane bound sac, or vesicle pinches off and moves the substance into the cytosol. Endocytosis includes phagocytosis (the entry of solids) and pinocytosis (the entry of liquids).

Equillibrium

Equal concentration gradient on each side of a membrane

Eukaryotes

Eukaryotes can be both unicellular and multicellular, have a nucleus which holds the DNA and other membrane bound organelles. They are larger and more complex. Example: animals, plants, fungi and protists

Exocytosis

Exocytosis is a type of vesicle transport that requires energy which refers to the movement of substances out of a cell using vesicles. In exocytosis, material are exported out of the via secretory vesicles. In this process the Golgi complex packages macromolecules into transport vesicles that travel to and fuse with the plasma membrane. This fusion causes the vesicle to spill its contents out of the cell. Exocytosis is important in expulsion of waste materials out of the cell and in the secretion of cellular products such as digestive enzymes or hormones.

Facilitated diffusion

Facilitated diffusion is diffusion across a plasma membrane which is facilitated by protein channels or carriers. It does not require chemical energy as the particles move down the concentration gradient. In facilitated diffusion the membrane transport proteins are specific for particular particles, therefore transport is selective meaning some particles are transported and others are not. These transport proteins can become saturated (fully occupied) as the concentration of transported substances increases. Facilitated diffusion is also faster than simple diffusion. Example: Large molecules, like glucose, and charged particles, like K+ and Cl-, need help to move across the cell membrane by diffusion.

Glycolipids

Glycolipids are made of lipids with chains of sugars attached and are invovled in cell to cell recognition

Glycoproteins

Glycoproteins are membrane proteins which play an important role cell recognition and the reception of cellular signals such as hormones. They consist of a protein with a chain of sugars (carbohydrates) attached that protrude into the external surroundings.

Internal Membranes

Many organelles are surrounded by membranes which are structural similar to the plasma membrane, but each have their own characteristics. Example: Nuclear membrane, mitochondrial membrane

Micelles

Micelles are formed when small amounts of phospholipids are placed in water causing them to form a 3D structure the tucks the hydrophobic tails away from the water so that only the polar heads make contact with water.

Spontaneously

Microscopic movements that continue to occur without any energy required. Example: molecules moving from an area of high concentration to an area of low concentration.

Mitochondria

Mitochondria are double membrane bound organelles found in almost all eukaryotic cells (not prokaryotes). The main functions of the mitochondrion is to produce the energy for the cell, ATP, through cellular respiration and to regulate cellular metabolism. For this reason the mitochondria are often called the powerhouses of the cell as they provide the cell with energy to preform it's normal functions. The number of mitochondria in a cell is related to the cell's energy requirements. Example: very active cells such as heart and muscle cells have many thousands of mitochondria.

Osmosis

Osmosis is a type of diffusion which involves the movement of water molecules across a semi-permeable membrane from an area of low solute concentration (dilute solution) to an area of high solute concentration (concentrated solution).This process of movement may only occur when two solutions are separated by a partially permeable membrane. Osmosis occurs when solutes cannot readily cross the membrane so instead water is drawn across to the more concentrated side to establish equilibrium.

Net Movement

Overall movement

Going down the concentration gradient

Particles going down the concentration gradient are particles moving without energy from an area of high concentration to an area of low concentration

Going up the concentration gradient

Particles going up the concentration gradient are particles moving from an area of low concentration to an area of high requiring energy.

Phospholipids

Phospholipids largely make up the plasma membrane they consist of two fatty acids (called the tail), a glycerol and a phosphate group (called the head). The head of the phospholipids is polar meaning it has a positive and negative side to it and is also hydrophilic meaning likes to be around water as water happens to also be a polar molecule. On the other hand the tail is non polar meaning it is neutral in charge and is hydrophobic meaning it dislikes being near water.

Turgid

Plant cells become turgid when they are placed in a hypotonic environment and the water is drawn into them causing the vacuole to expand, unlike animal cells plant cells will not burst in this case because of the rigid cells wall. The water instead will simply continue to flow into the cell until the internal fluid pressure equals the osmotic pressure drawing the water in, at which point no more water will enter.

Eukaryotic and Prokaryotic Cell Difference

Prokaryotes- small, larger surface area, no membrane bound organelles, nucleus, scattered ribosomes Eukaryotes- large, complex , small surface area top volume ratio, membrane bound organelles, ribosomes can be on ER or free, nucleus

Ribosomes

Ribosomes are very small complex organelles that don't have a membrane found within all living cells (eukaryotes and prokaryotes). They are composed of protein and ribosomal RNA (rRNA) and are responsible for protein production in the cell by linking amino acids together in the order specified by messenger RNA (mRNA) molecules. Ribosomes consist of two major components: the small subunit, which reads the RNA, and the large subunit, which joins amino acids to form a polypeptide chain. In eukaryotes many of the ribosomes are attached to internal channels, called endoplasmic reticulum.

Simple Diffusion

Simple diffusion is diffusion across a plasma membrane which is not facilitated meaning particles diffuse directly across the phospholipid bi-layer. Example: Small uncharged particles such as O2 or CO2 are able to diffuse directly across the phospholipid bilayer without assistance

Prokaryotes

Single celled organisms that do not have a nucleus and are small and simple, they also have a few internal structures which include DNA, Ribosomes, Cytosol, and a cell membrane as well as a cell wall in most of them. Example: bacteria, archaebacteria. *they are abundant in air, soil, water and on most objects

Golgi Apparatus

The Golgi apparatus also known as the Golgi body or Golgi complex or simply the Golgi, is an organelle made up of a series of membrane enclosed compartments found in most eukaryotic cells (not prokaryotic). Proteins synthesised in the endoplasmic reticulum are packaged into vesicles, which then fuse with the Golgi apparatus. These proteins are often modified in the Golgi before being packaged into membrane bound vesicles and sent to their destination. The Golgi can be thought of as similar to a post office: it packages and labels items which it then sends to different parts of the cell or out of the cell.

Solutes

Solutes are particles dissolved in water. Many solutes cannot readily cross the cell membrane, so instead water is drawn across to the concentrated side to establish an equilibrium

Cell Membrane

The cell membrane also known as the plasma membrane is found in all living things. This very thin, selectively permeable controls the exchange of materials, receives hormone messages and separates the cell from its surroundings. It can be described as a phospholipid bi-layer meaning that it is made from phospholipid molecules and has two layers. Some small, uncharged molecules are able to enter or exit the cell directly through this phospholipid bi-layer, however most substances cannot.

Cell Membrane Structure

The cell membrane is a semi-permeable or selectively permeable membrane (lets some particles through) which acts as a skin around the cell controlling the movement of substances into and out of the cell. It is composed of a phospholipid bilayer with proteins and other structures embedded into it. The proteins and lipids move laterally within the membrane structure in what is referred to as the fluid mosaic model. This structure in cells creates a barrier between the cell and it's environment. It physically separates the intracellular components of the cell from the extracellular environment that the cell is in.

Cell Wall

The cell wall is a rigid external structure surrounding the plasma membrane around the outside of plant, fungi, algae and most bacteria cells (animals do not have a cell wall). The cell wall of plants consist mostly of cellulose, whilst fungal and bacterial cell walls consist largely of chitin and peptidoglycan. It's function s to provide the cell with structure and protection and prevent lysis or bursting of the cell. The structure of a cell wall is quite porous, allowing many substances to move freely through it.

Cytoplasm

The cytoplasm is the cytosol and all the organelles inside the cell except the nucleus.

Cytoskeleton

The cytoskeleton is a network of protein filaments (flexible but strong) and microtubules (larger and more stiff) that extends throughout the cytoplasm and provides structure to all cells. The primary function of the cytoskeleton is to maintain the shape of the cell. It is also involved with the movement of vesicles and other organelles around the cell. In some cells, the cytoskeleton is involved with the mobility of the cell.

Endoplasmic Reticulum

The endoplasmic reticulum is a series of interconnected membrane-enclosed channels used to transport substances within most eukaryotic cells (not prokaryotic). There are two types of endoplasmic reticulum which are the rough and the smooth. The rough endoplasmic reticulum has ribosomes attached to it which synthesised proteins while the smooth endoplasmic reticulum lacks ribosomes and functions in the production of lipid and steroid hormones.

Intracellular Fluid

The fluid inside a cell.

Fluid Mosaic Model

The fluid mosaic model refers to the continuous movement of molecules that makes up the cell membrane and the proteins and other molecules which bob around in the bilayer. It is called the fluid mosaic model because there is movement or fluid and because it is interspersed with proteins and other molecules, like cholesterol which make a mosaic like structure.

Extracellular Fluid

The fluid outside the cells in a multicellular organism

Nucleus

The nucleus a large organelle found in eukaryotic cells surrounded by a double-layered nuclear membrane or nuclear envelope. In the nuclear envelope nuclear pores are found which help to nuclear pores are found help to regulate the transport of substances across the double membrane. The nucleus also contains a nucleolus which is the main structure in the nucleus containing most of the DNA and producing ribosomes which move out of the nucleus into the rough ER. In eukaryotes, most of the genetic material, it's DNA, is found in the nucleus in the form of chromosomes composed of the DNA and proteins. The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression, for this reason it is often referred to as the control centre of the cell. * this organelle is not present in prokaryotes

Phospholipid Bi-layer Membrane

The phospholipid bilayer of the plasma membrane is composed of two layers of phospholipids arranged in a double membrane. These phospholipids are arranged so that the hydrophilic heads form the outside and inside lining of the plasma membrane where they are in consist contain with water and the hydrophobic tails of the two layers of phospholipids meet in the middle where there are less to no water molecules.

Plasma Membrane

The plasma membrane is a selectively permeable barrier which lets some particles through but not all. Many different types of molecules can move across the plasma membrane however they do so in different ways depending on their properties such as: size and charge and whether or not the phospholipid bilayer is permeable to the substance. Example: for respiration glucose and oxygen must be let in through the cell membrane and waste products such as carbon dioxide and water must be removed. Also ions required for various functions may go through the plasma membrane and proteins made within the cell also must sometimes be released to carry out functions elsewhere in the organism.

Diffusion

The plasma membrane is a selectively permeable barrier which lets some particles through but not all. Many different types of molecules can move across the plasma membrane however they do so in different ways depending on their properties such as: size and charge and whether or not the phospholipid bilayer is permeable to the substance. Example: for respiration glucose and oxygen must be let in through the cell membrane and waste products such as carbon dioxide and water must be removed. Also ions required for various functions may go through the plasma membrane and proteins made within the cell also must sometimes be released to carry out functions elsewhere in the organism. Movement of articles from an area of high concentration to low concentration Movement of substance down the concentration gradient Passive transport- no energy required With or without plasma membrane

Osmotic Pressure

The pressure that causes free water molecules to move along the concentration gradient (osmotic gradient) across a semi-permeable membrane. It is caused by a difference in concentration of the solutions on each side of the membrane.

Plasma Membrane Surface Area

The surface area of the plasma membrane around a cell affects the rate of exchange that is possible between the cell and it's environment. This means that smaller cells are more efficient in exchanging matter with their environment as they have a larger SA:V ratio.

Surface Area to Volume Ratio

The surface area to volume ratio (SA:V) is the amount of surface are per unit volume of an object. The larger the object, the higher the surface area to volume ratio. The higher the SA:V ratio, the more efficiently the organisms can exchange materials such as wastes and nutrients with its environment.

Factors affecting rate of diffusion

The three main factors that affect the rate of diffusion across a membrane are: - Concentration- the greater the difference in concentration gradient, the faster the rate of diffusion. When the concentration is equal on both sides of the membrane the net diffusion is zero, even at high temperatures - Temperature- the higher the temperature, the higher the rate of diffusion. Increasing temperature increases the speed at which molecules move - Particle Size- the smaller the particles, the faster the rate of diffusion through a membrane

Vesicle Transport

There are two types of vesicle transport: endocytosis and Exocytosis which aid in the movement of molecules or particles that are too large to pass through the phospholipid bi-layer or to move through a transport protein. Endocytosis and Exocytosis occur through vesicles in the cytoplasm which move macromolecules or larger particles across the plasma membrane.

Proteins

There are various proteins found bobbing more slightly moving within the cell membrane. Some of these proteins called integral proteins are a permanent part of the plasma membrane structure meaning they are fixed to the inside of the cell and do not move while other proteins called peripheral proteins are a temporary part of the plasma membrane. Some forms of the integral proteins called transmembrane proteins span the length of both phospholipids and are involved in a number of important cellular and intracellular activates. Proteins altogether span the width of the membrane ,some only on the inner layer and some on the outer layer.

Increasing Cell Area

Three ways of changing the membrane surface area without changing the volume of the cell are: - Cell compartmentalisation - A flattened shape - Plasma membrane extensions

Vacuole

Vacuoles are membrane bound, liquid filled spaces that store dissolved enzymes and other organic and inorganic molecules. They occur in plant and fungal cells and some protist, animal and even a few bacterial cells but generally not in prokaryotic cells. The functions of vacuoles vary according to the cell type however it typically includes: Isolating materials that might be harmful to the cell, Containing waste products, Keeping plants cells turgid by becoming engorged with water, Maintaining an acidic internal pH and Exporting unwanted substances from the cell. In animal cells, vacuoles are usually small whereas in plant cells, vacuoles tend to be very large and can almost fill the cell.