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Biology

The study of life

Cells

Organelle Functions

Chloroplast

Site of photosynthesis

Cell Surface Membrane

  • Retains cellular contents
  • Forms permeability barrier between cytoplasm and extracellular environment
  • Controls the movement of substances
  • Enables cell to respond to extracellular signals
  • Enables cell to communicate with other cells

Cell Wall

  • Mechanical protection from injury
  • Gives plant cell a fixed shape

Cytoplasm

  • Where most cell activities occur
  • Transport materials within cell

Cell Vacuoles

Store substances within the cell
Maintains turgor pressure (plant cell)

Nucleus

  • Important for cell division
  • Controls cellular activities
  • Contains genetic information

Smooth Endoplasmic Reticulum

  • Synthesis of lipids and steroids
  • Detoxification

Rough Endoplasmic Reticulum

Membrane protein synthesis

Mitochondria

Site of aerobic respiration

Golgi Apparatus

  • Chemical modification of proteins
  • Sorting, packaging and secretion of proteins
  • Lysosome formation

Ribosomes

Site of protein synthesis

Comparison

Plant vs Animal

Chloroplast & cell wall in plants only
Centrioles in animals only
Central vacuole in plants, small temporary vacuoles in animals

Cells, Tissue, Organ, Organ System

Cell

Smallest unit of life

Tissue

A group of cells which work together to perform a specific function

Organ

Different tissues working together to perform specific function

System

Several organs working together for common purpose form system

Specialised Cells

Xylem Cells

Conduction and support

Long Hollow Tubes with No Cross Walls/Protoplasm

Create a continuously empty lumen

Narrow lumen

Transport of water by capillary actions

Ligin deposited on the walls

  • Waterproof to prevent loss of water
  • Strong to provide mechanical support and prevents collapse.

Root hair cells

Absorption of water and mineral salts

Long and Narrow Extension

Increases surface area to volume ratio of the cell which allows water and mineral salts to be more efficiently absorbed

Rich in mitochondria

Active transport of mineral salt against the concentration gradient into root hair cell

Red blood cells

Transport of oxygen

Presence of Haemoglobin

Contains red pigment called haemoglobin which transports oxygen from lungs to all parts of body

No Nucleus

Allows it to carry more haemoglobin ∴ more oxygen

Circular Biconcave Shape

Increases surface area to volume ratio for faster oxygen diffusion

Flexible Cell Surface Membrane

Allows red blood cells to squeeze through fine capillaries

Movement of Substance

Diffusion

Definition

The net movement of substances from a region of higher concentration to a region of lower concentration down the concentration gradient

Role

  • Nutrient uptake
  • Gaseous exchange

Osmosis

Definition

The net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane down a water potential gradient

Effects

Hypotonic: Higher water potential
Hypertonic: Lower water potential
Isotonic: Same Water Potential

Animal

Hypotonic

When an animal cell is placed in a hypotonic solution, water, water enters animal cell by endosmosis. Cytoplasm has lower water potential than external solution, water enters cell by osmosis. Cell expands in volume. Cell membrane is too delicate to prevent further expansion. Cell lyses and cell contents poured out.

Hypertonic

When an animal cell is placed in a hypertonic solution, water leaves the cell by exosmosis. Cytoplasm has higher water potential than external solution, water leaves the cell by osmosis. Cell shrinks in volume. Cell membrane crinkles and forms spikes in a process called crenation. Animal cell eventually dehydrates and dies.

Plant

Hypotonic

When a plant cell is placed in a hypotonic solution/water, water enters plant cell by endosmosis. Cell sap has lower water potential than external solution, water moves through cell wall and cell membrane and enters cytoplasm and vacuole by osmosis. Vacuole increases in size. Cell expands in volume. Cytoplasm and cell surface membrane pushed against and exerts pressure on cellulose cell wall. Water stops entering when inelastic cell wall exerts opposing pressure to resist further expansion. Cell becomes turgid.

Hypertonic

When a plant cell is placed in a hypertonic solution, water leaves plant cell by exosmosis. Cell sap has higher water potential than external solution, water leaves vacuole and cytoplasm and moves through cell membrane and cell wall by osmosis. Vacuole and cell shrink in size. Cytoplasm & cell membrane pull away from cell wall in a process known as plasmolysis. Cell becomes flaccid.

Active Transport

Definition

The movement of substances from a region of lower concentration to a region of higher concentration through a partially permeable membrane against the concentration gradient via a membrane-bound pump by using energy

Importance

  • Ion uptake by root hairs and
  • Uptake of glucose by cells in the villi

Nutrients

Water

Roles

  • Major component of protoplasm
  • Medium for chemical reactions
  • Transport agent
  • Essential component of body fluids
  • Regulates body temperature by using sweat

Carbohydrates

Info

Elements

C, H, O
H:O = 2:1

Types

Monosaccharides

  • Glucose
  • Galactose
  • Fructose

Disaccharides

  • Maltose
  • Lactose
  • Sucrose

Polysaccharides

  • Starch
  • Cellulose
  • Glucagen

Roles

  • Substrates for respiration
  • Structural carbohydrates
  • Convert to other organic compounds
  • Formation of nucleic acids
  • Synthesis of lubricants
  • Synthesis of nectar

Starch Test

Iodine Test

Add a few drops of iodine solution

Results

Blue-black: √
Yellow: X

Reducing Sugars Test

Benedict’s Test

Sucrose

  1. Add 4 drops of hydrochloric acid
  2. Boil for 2-3 minutes
  3. Let it cool
  4. Add sodium hydrogen carbonate to neutralise the acid

Go to solid/liquid

Solid

  1. Cut up into smaller pieces
  2. Add 2cm3 of water
  3. Stir
  4. Decant the water

Go to liquid step 2

Liquid

  1. Add 2cm3 of the food sample
  2. Add 2cm3 of Benedict’s solution
  3. Boil for 2-3 minutes

Results

Blue: X
Brick-red precipitate: √

Proteins

Info

Elements

C, H, O, N (Sometimes S)

Types

  • Amino acids
  • Polypeptides
  • Protein

Roles

  • Synthesis of new protoplasm for growth & repair
  • Synthesis of enzymes & some hormones
  • Formation of antibodies to combat diseases

Protein Test

Biuret Test

Solid

  1. Cut up into smaller pieces
  2. Add 2cm3 of water
  3. Stir
  4. Decant the water

Go to liquid step 2

Liquid

  1. Add 2cm3 food sample
  2. Add 2cm3 of Biuret solution

#Results
Blue: X
Purple: √

Lipids

Info

Elements

C, H, O
H > O

Components

  • Fatty acids
  • Glycerol

Roles

  • Source of energy
  • Insulation
  • Transport agent for some vitamins and vital substances
  • Component of cell surface membrane
  • Prevents water loss

Fats Test

Ethanol-emulsion Test

Solid

  1. Cut up the food into smaller pieces
  2. Add 2cm3 of ethanol
  3. Shake thoroughly
  4. Decant to 2cm3 of water

Liquid

  1. Add 2cm3 of food sample
  2. Add 2cm3 of ethanol
  3. Shake thoroughly
  4. Add 2cm3 of water

Results
Cloudy white emulsion: √
Clear: X

Enzymes

Human Nutrition

Organs

Mouth

Salivary glands

Produce and secrete saliva the mouth

Mucus and water

  • Moistens mouth & tongue and softens food
  • Facilitates swallowing

Salivary amylase

  • Breaks down starch into maltose
  • pH 7
     - Optimal for salivary amylase activity
  • Lysozyme
     - Destroys bacteria

Buccal cavity

Space enclosed by the mouth

Teeth

 Chewing action breaks up food into small pieces (mastication) to increase surface area to volume ratio for digestive enzyme action

Tongue

 Rolls food and saliva into small masses (boli) to facilitate swallowing

Oesophagus

 Narrow, muscular tube that joins the pharynx and the stomach uses peristalsis to push food forward

Stomach

Distensible, muscular bag

 Stretches when temporarily storing food, informs the brain when fully-distended

 Thick, well-developed muscular wall

Peristalsis churns the food to mechanically break them up and mix them forming chyme

 Wall has numerous pits

Gastric glands which produce gastric juice which contains hydrochloric acid, pepsin and renin

Hydrochloric Acid

  • Stops salivary amylase activity
  • Activates pepsinogen and prorennin
  • Provides acidic pH optimal for pepsin and rennin activities
  • Denatures proteins in food to exposes peptide bonds for hydrolysis by pepsin
  • Kills germs

Pepsin

Pepsinogen (Inactive) + HCl > Pepsin (Active)
Protein + Pepsin > Peptides

#Rennin
Prorennin (Inactive) + HCl > Rennin (Active)
Milk protein caseinogen (Soluble) + Rennin > Casein (Insoluble)
So it stays longer in the stomach

Lined by mucus layer

Protection against damage by hydrochloric acid in gastric juice

Sphincters

The lower oesophageal sphincter connects stomach to the oesophagus and the pyloric sphincter connects stomach to the small intestine, they control the movement of food into and out of the stomach

Small Intestine

Parts

  • Duodenum (U-shaped)
  • Jejunum
  • Ileum (Much-coiled)

Intestinal Juice

  • Maltase
  • Sucrase
  • Lactase
  • Erepsin (Peptidase)
  • Lipase

Gall Bladder

Stores bile produced by the liver which emulsifies fats increasing the surface area to volume ratio

Pancreas

Pancreatic Juice

  • Insulin
  • Glucagon
  • Amylase
  • Trypsin/Chymotrypsin
  • Lipase
  • Nuclease

Large Intestine

Colon

  •  Absorbs H2O, mineral salts and vitamins from undigested food
  • Peristalsis of colon wall propels undigested food to the rectum

Liver

Liver Vessels

Hepatic Portal Vein

Nutrient-rich blood from small intestine to liver

 Hepatic Artery

Oxygenated blood from heart to liver

Hepatic vein

Deoxygenated blood from the liver to the heart

Functions

  • Deamination
  • Detoxification
  • Regulation of Blood Glucose Concentration
  • Protein synthesis
  • Bile production
  • Iron storage

Effects of Alcohol

  • Depressant
  • Reduced self-control
  • Slower reaction time
  • Excessive stomach acid secreted
  • Replaces liver cells with fibrous tissue by cirrhosis
  • Social Implications

Zoom in

Peristalsis

The rhythmic wave-like antagonistic contraction and relaxation of smooth muscle layers, outer longitudinal muscles and inner circular muscles, causing dilation and constriction to mix and propel food

Villi

Increase surface area to volume ratio

 1-cell thick epithelium

Smaller diffusion distance, has microvilli to increase surface area to volume ratio

 Blood and Lymph Capillaries

Maintain concentration gradients

Blood Capillaries

Transports glucose and amino acids

Lymph Capillaries (Lacteals)

Transports lipids

Plant Nutrition

Leaf Structure

External

Network of Veins

Veins carry water and mineral salts to the cells in the lamina and carry manufactured food from these cells to other parts of the plant

Lamina

The lamina has a large flat surface compared to its volume. This enables it to obtain the maximum amount of sunlight for photosynthesis
A large, thin lamina also means that carbon dioxide can rapidly reach the inner cells of the leaf

Leaf Arrangement

  • Leaves are always organised around the stem in a regular pattern
  • Ensures that the leaves are not blocking one another from the sunlight and that each leaf receives sufficient sunlight

Petiole

The petiole holds the lamina away from the stem so that the lamina can obtain sufficient sunlight and air in come leaves

Internal

Upper Epidermal Cells

  • Single layer of closely packed cells
  • Covered on the outside by waxy and transparent cuticle.
  • Epidermis protects the inner regions of the leaf

Palisade Mesophyll Cells

  • One or two layers of closely packed, long and cylindrical cells with their long axes at right angles to the epidermis
  • Contain numerous chloroplasts

Spongy Mesophyll Cells

  • Irregularly shaped cells that are loosely packed with numerous large intercellular air spaces
  • Fewer chloroplasts than palisade mesophyll cells
  • Cells covered with thin moisture film
  • Contain vascular bundle, xylem and phloem

Lower Epidermal Cells

  • Single layer of closely packed cells beneath mesophyll
  • Covered by an outer layer of cuticle to reduce water loss

Guard Cells

Day

  • Increase water potential
  • Produce glucose
  • Convert light to chemical energy to be used to pump K+ ions into guard cells from neighbouring epidermal cells by active transport
  • Water from other cells enter the guard cells by osmosis
  • Swell and become turgid
  • Since they have a thicker cellulose wall on one side of the cell, the swollen guard cells move further apart and pull the stoma open

Night

  • Lower water potential
  • Sugar is used up
  • K+ ions diffuse out
  • Water leaves the guard cells by osmosis
  • Become flaccid and the stoma closes.

Stomata

Minute openings usually found on the lower epidermis

Adaptations

  • Petiole
  • Thin lamina
  • Large flat surface
  • Waxy cuticle on upper and lower epidermal layers
  • Stomata present mostly in lower epidermis
  • Chloroplasts containing chlorophyll
  • More chloroplasts in upper palisade tissue
  • Inter-connecting system of air spaces in mesophyll
  • Veins containing xylem and phloem

Photosynthesis

Requirements

  • Carbon Dioxide
  • Water

Products

  • Glucose
  • Oxygen
  • Water (Optional)

Chemical Equations

Light-Dependent

Light energy -> Chemical energy
12H2O (Photolysis) -> 6O2 + 24H

Light-Independent

6CO2 + 24H (Chemical energy) -> C6H12O6 + 6H2O
(Enzyme-controlled reactions)

Overall

6CO2 + 12H2O > C6H12O6 + 6O2 + 6H2O

Simplified

6CO2 + 6H2O > C6H12O6 + 6O2
Carbon dioxide + Water > Glucose + Oxygen

#Limiting Factors

  • Light intensity
  • Carbon dioxide concentration
  • Temperature