Five-Kingdom Classification and Microorganisms | Cells and Membrane Transport | Enzymes | Digestion

Five Kingdom Classification and Microorganisms

Taxonomy: The science of naming and classifying organisms. (avoid confusion, standardization)

Classification System (Hierarchy of classification): Kingdom, phylum, class, order, family, genus, species (more similarities, fewer differences)

Mnemonics: K-Pop Culture Only For GirlS OR King Phillip Cuts Off Friend’s Giant Stick (popular) OR Katy Perry Chews On Friend’s Giant Sausage

Binomial Nomenclature:

Genus + Species Generic name (capital), specific name (lower case) underlined (handwriting), itacilized (printing) eg. Homo sapiens Unspecified species: Genus+ [sp./spp.] (e.g. Escherichia sp.)

Dichotomous key for identifying organisms

2 alternatives for each step in the key (usually distinguishing features; external features so that it is easily seen/identifiable)

Five Kingdoms of Classification

Monera

`Prokaryotic (no nuclear envelope: main DNA strand not contained inside a nucleus. Single loop DNA) Peptidoglycan cell wall may be present Slime coat (made of lipopolysaccharide) may be present. Contains a plasma membrane and cytoplasm Mostly saprophytic or parasitic. (a few are autotrophic) Shapes: coccus, bacillus, spirillum, filament, chain Reproduction:

Asexual reproduction: binary fission (identical genetic material in parent and offspring)Sexual reproduction: (i) conjugation: male cell passes DNA to female cell by means of sex pilus (conjugation tube). Direct contact

between both cells is necessary (ii) transformation: taking up DNA released by dead bacteria(iii) transduction: DNA transferred between bacterial cells by bacteriophage.

*(ii) and (iii) no direct contact between cells is required Antibiotic mechanism

Wide spectrum of drugs available (drug inhibits peptidoglycan cell wall production) Drug causes bacteria cell to rupture

Bactericidal—antibiotics kill pathogens directly Bacteriostatic—prevents pathogens (microbes) from reproducing, leaving immune system to kill existing microbes Antibiotic resistance:

(i) Mutation Mutation is a change in DNA that can sometimes cause a change in the gene product, which is

the target of the antimicrobial (ii) When a susceptible bacterium comes into contact with a therapeutic concentration of antimicrobials(iii) Destruction or inactivation

Many bacteria possess genes which produce enzymes that chemically degrade or deactivate the antimicrobial, rendering them ineffective against the bacterium.

Here the antimicrobial is either degraded or modified by enzymatic activity before it can reach the target site and damage the bacterial cell.

(iv) Efflux Certain bacteria can often become resistant to antimicrobials through a mechanism known as

Efflux. An efflux pump is essentially a channel that actively exports antimicrobial and other compounds

out of the cell. The antimicrobial enters the bacterium through a channel termed a porin, and then is pumped

back out of the bacterium by the efflux pump. By actively pumping out antimicrobials, the efflux pumps prevent the intracellular accumulation necessary to exert their lethal activity inside the cell.

(v) Genetic transfer:

Conjugation Conjugation is mediated by a particular kind of circular DNA called a plasmid, which

replicates independently of the chromosome. Many plasmids carry genes that confer resistance to antimicrobials. When two cells are in close proximity to each other, a hollow bridge-like structure,

known as a pilus, forms between two cells. This allows a copy of the plasmid, as it is duplicated, to be transferred from one

bacterium to another. This enables a susceptible bacteria to acquire resistance to a particular antimicrobial

agent. Transformation

During this process, genes are transferred from one bacterium to another as “naked” DNA.

When cells die and break apart, DNA can be released into the surrounding environment. Other bacteria in close proximity can scavenge this free-floating DNA, and incorporate it into their own DNA. This DNA may contain advantageous genes, such as antimicrobial resistant genes and benefit the recipient cell.

Transduction In this process, bacterial DNA is transferred from one bacterium to another inside a

virus that infects bacteria. These viruses are called bacteriophages or phage. When a phage infects a bacterium, it essentially takes over the bacteria's genetic

processes to produce more phage. During this process, bacterial DNA may inadvertently be incorporated into the new

phage DNA. Upon bacterial death and lysis (or breaking apart), these new phage go on to infect other bacteria.

This brings along genes from the previously infected bacterium.

Fungi

Found almost everywhere Chitin cell wall Mostly multi-cellular except yeast (most visible by naked eye) No true root (mycelium), with no stem or leaf Cells are made up of a network of branching tubes known as hyphae (plural: mycelium) Absorption feeders Eukaryotic (Presence of nuclear envelope) Contains cytoplasm Cenocytic (Presence of multiple nuclei) Some fungi are parasitic (ringworm, athlete’s foot in humans) Mainly saprophytic (grow on decaying matters). Rhizoids release digestive enzymes to the food. Food stored as glycogen. Reproduction (dependent on type of fungus and environmental conditions):

Asexual: (a) budding: new organism developing from an outgrowth of another(b) fragmentation: hyphae breaks off and grows as new individuals (lichen)(c) sporesSexual (combination of gametes)

Animalia

heterotrophic Multi-cellular Most can move (locomotion)

Plantae

Autotrophic (chloroplasts) has true leaves, stems and roots

Protoctista

contains features which do not fit into other kingdoms eukaryotic in nature true living cells Algae:

-unicellular or multi-cellular organisms that live mainly in water-plant-like organisms. However, no true root, and have no stem or leaf. -autotrophic (photosynthetic, contain chlorophyll or other kinds of photosynthetic pigment)

Protozoa (amoeba, paramecium): -unicellular organisms that are free living, mainly in water-heterotrophic-parasitic (malaria, amoebic dysentery)

Reproduction in protoctistas: -sexually: gametes-asexually: binary fission

Viruses

0.1 µm in length (Visible only under electron microscope) No protoplasm Protein coat called a ‘capsid’ that surrounds nucleic acid (genetic material) More advanced viruses have bi-lipid envelope that surrounds capsid, and glycoproteins, which are proteins and

carbohydrate compounds. Will have either RNA (Ribonucleic acid) or DNA but not BOTH Most viruses are pathogenic Shapes: Helical, Icosahedral, Complex Reproduction:

Virus locates suitable host cell and attaches to surface of cell/is ingested into host cell. Virus releases genetic material into the cell. Normal cell processes in host cell are shut down Cell begins to use the viral genetic material to make viral proteins Virus uses cell’s energy and materials to produce the nucleic acid and capsomeres to make numerous

copies of the original virus. Once these new viral particles are assembled, host cell ruptures and releases new virus to infect

neighbouring cells.

***Differences between prokaryotes and eukaryotes

Basis for comparison Prokaryotic cells Eukaryotic cellsSize Small cells (< 5um) Larger cells (> 10um)Types of cell Mostly unicellular Mostly multicellularPresence of nuclear envelope No nucleus (no nuclear envelope) or

any membrane-bound organelles (ie. no mitochondria, endoplasmic reticulum, golgi apparatus)

Have nucleus and membrane bound organelles

How the DNA are organized DNA is circular, without proteins (histones)

DNA is linear, associated with proteins (histones), and is organized into chromosomes; the chromosomes are bounded by a nuclear envelope (a double membrane structure)

Size of ribosomes Have ribosomes (70S) (ribosomes are non-membrane bound organelles- they comprise of RNAs)

Have ribosomes (80S)

Vaccinations

A vaccination is the preparation of an attenuated strain/pathogen, such as a bacterium or a virus, or a portion of the pathogen’s structure, that upon administration stimulates antibody production and cellular immunity against the pathogen, but is incapable of causing severe infection. (It prevents/ ameliorates the effects of infection by many pathogens)

Aseptic Techniques

Precautions

70% ethanol—kills germs

Autoclave—kills off all possible micro-organisms/microbes present in agar medium (prevents contamination)

It is also necessary to flame the bottle neck so that the liquid agar is still sterile when poured out. (kills off any possible microbes found on the bottle neck)

The plates are placed upside down during the incubation to prevent condensate formed on the lid from falling back onto the agar surface and thus diluting/spreading the colonies. This also minimizes contamination from extraneous bacteria.

Describing colonies

Specify:

a) Form; shape of colony e.g. circular, irregular and spreading, filamentous, rhizoid b) Size (diameter) c) Number of colonies d) Colour, includes optical characteristics such as opaque, translucent, clear etc. e) Optional: Surface, texture, elevation, margin

Factors affecting bacterial growth

a) pH b) Oxygen c) Temperature (Most microbes thrive best at 37°C as it is the optimal temperature for enzymes within bacteria to

metabolise sugars and nutrients in agar.) d) Sufficient nutrients e) *Concentration of antibiotics (if there is)

Cells, Diffusion and Osmosis

Cells are the building blocks of life

Cell theory states that:

a) All living organisms are made up of one or more cellsb) Cells are the basic unit of life.c) All cells come from division of pre-existing cells.

Cells can exist as unicellular or multi-cellular organisms.

Cell →Tissue → Organ → Organ system → Organisms

The cells in a multi-cellular organism are differentiated/modified for specific/specialized functions. This division of labour allows cells to perform their specific functions efficiently and effectively (at the same time). In fact, there is also division of labour in uni-cellular organisms (at the cellular level).

Red blood cell

No nucleus (RBC able to carry more haemoglobin → increase oxygen carrying capacity per RBC) Circular biconcave shape (increases surface area: volume of cell →oxygen can diffuse faster into and out of the cell

at a faster rate. Flexible to squeeze through small capillaries

Muscle cell

Long, with many protein fibers in the cytoplasm. Fibers can shorten the cell when energy is available → Muscle cell contracts allowing movement.

Smooth muscle cells (involuntary muscles) Skeletal muscle cells (most abundant; voluntary muscles; well organized striations) Cardiac muscle cells (voluntary muscles; less organized striations)

Xylem Vessel

Xylem cells are laid end to end. Long hollow tubes are formed (water and mineral salts are conducted from roots up to leaves and stems) Xylem vessels do not have cross walls (allows water to move easily through lumen of xylem vessels; continuous path

of water transport) Lignin is deposited (in rings, spiral, pitted) on walls of xylem vessels (walls are strengthened → provides structural

support)

Root hair cell

Long and narrow projection (increases surface area: volume ratio of cell; increases efficiency of absorption of water and minerals from soil)

Central vacuole contains concentrated cell sap, which helps to draw water and minerals into the cell from the soil by osmosis.

Certain cells have pseudopods (false feet) to move around (more commonly found in uni-cellular organisms). A pseudopods occurs when the cell temporarily pushes its plasma membrane out in one direction, and then pulls it in, causing the cell to ‘crawl’. The cell does this by pushing the actin network (mesh of structural fibers part of the cell’s skeleton) outwards, and then resumes its original shape.

Cellular metabolism is the process of converting cell materials into energy. The two main metabolism routes are cytoplasmic and mitochondrial metabolism. In cytoplasmic metabolism, the cell performs glycolysis within the cytoplasm of the cell through various enzymes, in which glucose is converted to pyruvate and some ATP (2). However, mitochondrial metabolism is the process of using the pyruvate generated by glycolysis to generate an electron transfer chain, which creates a charge gradient. This gradient is used to turn a molecular generator which creates large amounts of glucose within the mitochondria (38).

Cytoplasmic streaming, also known as cyclolysis, is the delivery of nutrients, metabolites, genetic information and other materials to all parts of the cell. Chloroplasts may be moved around with the stream, possibly to a position of optimum light absorption for photosynthesis.

Characteristics of cell parts

Plasma membrane (Cell membrane)

Partially permeable Regulates substances that enter and leave the cell Separates cell interior/cell contents from its outer-surroundings Made up of a wide variety of biological molecules, primary proteins and lipids (fatty acids are a subset of lipids),

which are involved in several different processes in the cell. Lipids form the majority of the membrane in what is called a “lipid bilayer”. Phospholipids have hydrophilic head and hydrophobic tail, so when they are in water they all flip to face the same

direction.

Cytoplasm

Fluid part of cell that is enclosed within plasma membrane Medium in which all cell activities occur Contains enzymes and organelles

NOTE: Cytoplasm =/= Cytosol (Cytosol refers to intracellular fluid)

Cell wall

Only for plant cells Fully permeable Cellulose cell wall (for plant cells) Provides plant cell with structural support Protects plant cell from injury

NOTE: When stating cell wall, remember to specify what TYPE (peptidoglycan, chitin, cellulose)

Organelles

Centriole

Found in animal cells (absent in plant cells) A pair of tiny structures found close to the nucleus. Organize the assembly of microtubules (cytoskeleton) during cell division.

Nucleus

Contains nucleolus which produces rRNA (ribosomal RNA) and ribosome components Chromatin—contains genetic information of the cell Nuclear envelope—regulates substances entering and leaving the nucleus. Controls all cellular activities

Mitochondrion

Enclosed by double membrane Inner membrane folding called cristae to increase its surface area so as to produce more energy in the cell. Has its own DNA genome (Mitochondria SNA/mtDNA) Site of aerobic respiration to produce energy (used by the cell to perform cellular activities) Released energy is temporarily stored as ATP (Adenosine Triphosphate)

Ribosomes

Found in two places in the cell Attached to rough endoplasmic reticulum—synthesizes proteins that are transported out of the cell Ribosomes which are lying freely in the cytoplasm synthesizes proteins that are within cytoplasm of the cell. Also found in prokaryotes 70S type (prokaryotic): comprise of RNA and proteins. Not bounded by membrane.

Endoplasmic Reticulum (ER)

Network of tubules, vesicles and cisternae (sac-like structures) within cells. Smooth ER:

Synthesis of lipids and steroids Metabolism of carbohydrates Regulation of calcium concentration Drug detoxification Attachment of receptors on all membrane proteins, and steroid metabolism Increased surface area for the action or storage of key enzymes and the products of these enzymes.

Rough ER: Studded with protein-manufacturing ribosomes that give it a rough surface area.

Golgi apparatus

Packaging and shipping plant in the cell. Can tag vesicles and proteins and then carried to correct destination, especially proteins that are being packaged to

leave the cell through exocytosis. Primarily modifies proteins (right structure) delivered from the RER before secretion. Involved in the transport of lipids around the cell and the creation of lysosomes

Vacuoles

Fluid-filled space enclosed by a membrane May contain water and organic molecules Animal cell has many small vacuoles but plant cell usually has one or a few, large central vacuoles (containing cell

sap), enclosed by a membrane called tonoplast Cell sap contains dissolved substances such as sugars, mineral salts and amino acids.

Chloroplasts

Contains light sensitive pigments such as chlorophyll (to trap light and photosynthesise) Inner membrane of chloroplast is arranged in flattened membranous arcs called thylakoids Thylakoids then form into stacks known as gama Stroma is the space outside the thylakoid Essential proteins for photosynthesis, or the production of carbohydrates are located in the stroma.

Membrane Transport

*When comparing plant and animal cells, always state: with respect to (cell part), the plant cell has (cell part) but an animal cell does not.

Membane Transport

Diffusion

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration ORThe net movement of particles down a concentration gradient (particles no longer move at absolute zero)

Particles continue to move even after particles reach equilibrium (dynamic and random motion) Occurs passively, without external energy requirements Factors affecting diffusion:

Concentration gradient (concentration difference between regions of high concentration and low concentration)

The steeper the concentration gradient, the faster the rate of diffusion Cross sectional area (surface area: volume) through which diffusion occurs

The amount of nutrients a cell can take in depends on the amount of surface area Similarly, the amount of waste that can be expelled from a cell depends on the surface area. However, surface area and amount of nutrients do not increase as rapidly and exponentially as

volume. Thus, as the size increases, at a certain point cell will not be able to get enough nutrients →

surface area: volume not large enough for diffusion to occur. Temperature

↑ temp. → ↑ energy → ↑ diffusion Molecular weight of a substance (less dense substance → faster diffusion) Distance through which diffusion occurs

Osmosis

Osmosis is the movement of particles from a solution of higher water potential to a solution to lower water potential through a partially permeable membrane.

Occurs passively, without external energy requirements Water potential: Tendency of water to move from one place to another Dilute solution: ↑ water potential Concentrated solution: ↓ water potential Reverse osmosis (process requires a force)

Comparison of Solutions

Terminology DescriptionIsotonic Two solutions are isotonic with respect to each other if they have the same solute concentration and thus

equal water potential (there is no net movement of water molecules since the number of water molecules that are moving into the cell is the same as the number of water molecules moving out of the cell.)

Hypertonic A solution is hypertonic with respect to the other if it is more concentrated and hence has a lower water potential

Hypotonic A solution is hypotonic with respect to the other if it is less concentrated and hence has a higher water potential.

Effect of Osmosis on Plant and Animal Cells

Plant Cells Animal CellsHigher water potential When a plant cell is immersed in a

solution of higher water potential, water enters the cell via osmosis through the partially permeable plasma membrane. This causes the vacuole of the plant cell to increase in size, pushing against the cell wall. The cell wall exerts opposing pressure against turgor pressure. As a result, the plant expands and become turgid.

…. (refer to plant cell)Animal cell swells and may burst/lyse (no cell wall to protect it)

Lower water potential When a plant cell is immersed in a solution of lower water potential, water leaves the cell via osmosis through the partially permeable plasma membrane. This causes the vacuole of the cell to decrease in size, and the cytoplasm shrinking away from the cell wall

Cell shrinks and little spikes appear on cell surface membrane (crenation)

(plasmolysis). In less severe cases, the plant cell may be simply flaccid (soft, not firm).NOTE: The term “plasmolysed” can only be used if the cell is seen under a microscope.

Active Transport

Active transport is the movement of substances from a region of lower concentration to a region of higher concentration (against a concentration gradient), usually across a partially permeable membrane)

Requires energy from respiration in the form of ATP Usually carried out by protein pumps embedded in the membrane Rate of transport depends on availability of energy and density of protein pumps.

*When answering questions regarding osmosis/diffusion,

Specify the water potential status (e.g. Solution A has a higher water potential than the cell cytoplasmic content). Identify the process (e.g. Water entered the cell via osmosis through the partially permeable membrane) Conclude the aftermath (e.g. the cell expanded and lysed)

Enzymes

Enzymes are… 1. Biological catalysts 2. Made of protein 3. Alter the rate of chemical reactions 4. WITHOUT being chemically changed at the end of the reactions.

Anabolic reactions—synthesis of complex substances from simpler ones Catabolic reactions—breaking down of complex substances into simpler ones.

NOTE: Enzymes catalyse the chemical reactions, but they do not cause reactions to occur.For instance, sometimes during chemical reactions in the cells, hydrogen peroxide is produced. This is poisonous to the body tissues and has to be broken down to harmless water and oxygen in the cells. Even without the help of enzymes, the hydrogen peroxide will still be broken down, but this is an extremely slow process that may eventually intoxicate the cells.

Enzymes are required in minute amounts (they can be re-used again and again) Enzymes are highly specific. (e.g. amylase found in saliva will act only on starch and not proteins. Similarly, lipase

found in the small intestine will only act on fats). Lock and key hypothesis (Enzyme+ substrate → enzyme-substrate complex → product + enzyme

Factors affecting enzyme activity

Temperature Enzymes are inactive at very low temperatures. Enzymes have an optimum working temperature. They are most active at

this temperature. Beyond the optimum working temperature, enzyme activity decreases.

Enzymes are denatured at high temperature, that is, its activity is completely destroyed (the enzyme loses its shape and thus cannot bind to its specific substrate → no catalysis of recation)

Temperature graph/curve is asymmetrical. pH level

Enzymes are denatured at extreme pH. Enzyme have an optimum working pH. Symmetrical graph

Enzyme and substrate concentration

When the concentration of substrate increased, there is a corresponding increase in reaction rate (but only when the substrate concentration remains comparatively small). This is because at low substrate concentrations, many of the active sites of the enzymes are unoccupied and the restricted supply of substrate molecules largely determines the reaction rate.

When larger substrate concentrations are used, however, the reaction rate becomes less dependent upon the concentration of the substrate but tends towards a fixed maximum (constant) determined by the amount of enzyme present. This is because at high substrate concentrations, almost all of the active sites of the enzymes are occupied, thus in order to further increase the rate of reaction, the amount of enzyme used has to be increased,

When the enzyme concentration is increased, there will be a proportionate increase in the maximum rate.

Co-enzymes and Enzyme inhibitors

Co-enzymes

Co-enzymes are non-protein compounds. Many of them are Vitamin B complex. Substrate molecules will not fit correctly at the active centre and three will be no catalytic action unless the cofactor

molecule is also present. (not specific)

Enzyme inhibitors

Enzyme inhibitors are molecules that bind to enzymes and decrease their activity. The binding of an inhibitor can stop a substrate from entering the enzyme's active site and/or hinder the enzyme from catalyzing its reaction.

Inhibitor binding is either reversible or irreversible. Irreversible inhibitors usually react with the enzyme and change it chemically. These inhibitors modify key amino acid

residues needed for enzymatic activity. In contrast, reversible inhibitors bind non-covalently and different types of inhibition are produced depending on

whether these inhibitors bind the enzyme, the enzyme-substrate complex, or both.

Read more: http://wiki.answers.com/Q/Difference_between_reversible_and_irreversible_inhibitors#ixzz28Uz3ninb

Animal Nutrition

Key Definitions:

Animal Nutrition: Process of consuming food and converting it into building blocks of living matter. Digestion: Breakdown of food substances into small soluble molecules that can be absorbed. Physical Digestion: Mechanical break-up of food into smaller particles Chemical Digestion: Enzymatic break-down of large molecules of food into small soluble molecules Ingestion, Digestion, Absorption, Assimilation and Egestion:

Ingestion is defined as the process of taking food into the body through the mouth (consumption, eating)Digested food substances have to be absorbed into the circulatory system and assimilated by the body. Egestion is defined as removal of undigested matter from the body.

Functions of the Human Digestive System (alimentary canal) and its accessory organs

Part Function Action of enzymesMouth/Buccal cavity (pH=7)

Teeth Tongue Salivary Glands

Teeth grinds and breakdown food (mastication)

Tongue rolls food into bolus before swallowing takes place

Saliva dilutes and moistens food

Mucin softens food Chewing action breaks

down larger pieces of food into smaller pieces, increasing S.A:V of food for chemical digestion to occur

Salivary amylase (ptyalin) in saliva catalyzes the digestion of starch into maltose.

Pharynx Bolus is pushed into pharynx, then into the oesophagus

Oesophagus Waves of muscular contraction (peristalsis) push food from pharynx

to stomach Contraction: gut wall

contracts; food is pushed forward.

Relaxation: gut wall dilates and food can enter.

Stomach (pH=2) A muscular bag with thick stretchable muscle walls

Muscular walls churn and break up food (continual contraction and relaxation of stomach muscle walls generate churning action that further breaks down food particles; higher SA:V; faster rate of chemical digestion

Secrete gastric juices (pH=2) which mixes with food to form chyme.

Stores food for 2-6 hours

Pepsin(a protease) catalyzes the digestion of proteins into peptides

Hydrochloric acid: provides acidic

conditions for action pepsin

denatures salivary amylase and stops its action.

Converts inactive form of enzyme pepsinogen to active form pepsin.

No carbohydrate digestion in stomach (pH is too low for action of amylase)

Gastric juice: Dilute solution of

hydrochloric acid and digestive enzymes pepsin (protease)

1Small Intestine (pH=9) Duodenum Jejunum Ileum

Intestinal wall contains glands that secrete enzymes, including protease, maltase and lipase; adapted for absorption of digested food product and water

Allows pancreatic juice to act on the food

Absorption of digested food occurs in the small intestine.

Release of chyme into the duodenum is controlled by the opening and closing of a valve known as a pyloric sphincter.

94% of water absorbed through the small intestine.

Protease (trypsin) catalyzes the digestion of peptides and proteins (that escape digestion in the stomach) into amino acids.

Maltase catalyzes digestion of maltose into glucose

Lipase catalyzes digestion of lipids (fats) into fatty acids and glycerol

Pancreas Secretes pancreatic juice, which flows into the duodenum through a pancreatic duct.

Enzymes in pancreatic juice include amylase, lipase and protease, which catalyze the digestion of food in the small intestine.

Amylase catalyzes digestion of starch (that escaped digestion in the mouth) into maltose.

Lipase (together with those found in the intestinal glands) catalyzes the digestion of lipids into fatty acids and glycerol

Protease (together with those found in the intestinal glands) catalyzes the digestion of proteins into amino acids

Liver and gall bladder Liver produces green bile (alkaline; contains bile salts and bile pigments)

Gall bladder stories the bile (temporarily)

Bile flows through the bile duct and empties into the duodenum

Bile emulsifies fats (breaks it down into smaller particles or droplets) so that a larger surface area of fat droplets is made available for enzyme action in the small intestine

Large Intestine Absorbs water and minerals from undigested food passed down from the ileum.

Rectum stores undigested matter temporarily in the rectum before it is eventually

expelled through the anus when the rectum contracts.

1small intestine (adaptations to facilitate absorption)

a) Large surface area ↑ rate of absorption Inner walls of small intestine have numerous folds. Inner walls are also lined with numerous minute, finger like projections; known as villi. Epithelial cells of the villi has numerous microvilli. Increase the number of brush border enzymes on the cell surface.

b) Thin walls and membranes; facilitate diffusion Epithelium of the villi is only on cell thick.

c) Long; increases time for absorption. d) Many capillaries to carry away absorbed substances (steep concentration gradient for diffusion)