IGCSE COMBINED SCIENCE Seven Life Processes

IGCSE COMBINED SCIENCE

Biology: B1 Cells

B1.01 Characteristics of living things

Seven Life Processes

Movement: An action by an organism or part of an organism causing a change in

position/place

Respiration: Chemical reactions in the cells that break down nutrients molecules to release

energy for metabolism

Sensitivity: Ability to detect & respond to changes in the environment

Growth: Permanent increase in size

Reproduction: the processes that make more of the same kind of organism

Excretion: Removal from organisms of waste products of metabolism, toxic materials &

substances in excess of requirements

Nutrition: Taking in minerals for energy, growth & development

B1.02 Cells

Cells Tissues Organs Organ Systems Organisms

Importance

Simplest part of a living structure that can operate as an independent unit

Made up of organelles

Structures inside living cells that carry out specific functions leading to the survival of

the cell (eg. Nucleus)

Magnification

Hand lens magnifies up to? 10

Good light microscope magnifies up to ? 1500

Electron microscope magnifies up to? 10 million

Magnification =

Cell Structure

Part of a cell

Can be observed by Structure & functions

Cell Membrane

Light microscope

(Plant & Animal cell)

Thin layer of protein & fat Partially permeable Controls what goes in & out of the cell (ie. movement of glucose) Allows simple substances( , , ) to pass

2 22

Surrounds the cytoplasm

Cell Wall (Plant cell only)

Light microscope

Made of cellulose (type of polysaccharide) Fully permeable (little space between fibres) Protection against injury for the plant cells Gives the cell its shape Prevents the plant from bursting when too much water enters it

Nucleus

Light microscope

(Plant & Animal cell)

Controls all cellular activities Contains genetic information arranged in chromosomes (made of

DNA) Chromosomes can only be seen when the cell is dividing; become short & thick

Cytoplasm

Light microscope

(Plant & Animal cell)

Contains cytosol (semi liquid 70% water) Organelles found here Respiration & chemical reactions occur

Vacuole

Light microscope

Sac inside the cell stores salts & sugars

(Plant & Animal cell)

Chloroplasts (Plant cell only)

Electron microscope

Keeps the shape of the cell Plant cells: single large vacuole containing cell sap (liquid

containing sugars & other substances dissolved in water) Animal cells: many small vacuoles (vesicles) containing

nutrients/water

An organelle containing chlorophyll Absorbs energy from the sunlight (used for photosynthesis)

Site of photosynthesis

Specialised cells

Type of cell

Location

Function

Adaptation

Image

Palisade Cell (P)

Beneath the epidermis of a leaf

Photosynthesi s

Regular shape Many can fit in a small space

Large vacuole restricts chloroplasts to a region of periphery; closer to the outside of the cell (absorb more sunlight)

Cell wall is very thin for fast diffusion

Root Hair Cell (P)

Near the end of the plant roots

Absorb water & mineral salts

Large surface area increase rate of absorption

Filled with mitochondria; specialised for active transport of mineral ions from the soil to roots

Presence of sap vacuole lowers its water potential for water to be absorbed by osmosis

Red Blood Cell In the blood Transport

(A)

of mammals oxygen

Biconcave shape increases the surface area to volume ratio which allows faster absorption & release of dissolved oxygen

Doesn't contain a nucleus; more space to store haemoglobin

Ciliated Epithelial Cell (A)

Lining of the trachea & bronchi

Move mucus upwards

Thin layer of moving `hairs'(cillia) traps & mozes dust & bacteria

B2: Movement in & Out of Cells B2.01 Diffusion Net movement of molecules & ions from a region of higher concentration to a region of lower concentration down a concentration gradient as a result of their random movement Until equilibrium is reached Equilibrium: when the concentrations are equal Concentration gradient: difference between the concentration of molecules in 2 regions Only small molecules (eg.2&2) can cross the cell membrane by diffusion Doesn't require any energy from the cell Factors influencing a higher rate of diffusion: Higher temperature Provides the particles with more kinetic energy Larger surface area Larger area to act on Larger concentration gradient Larger difference in the high & low concentrations increases diffusion rate Higher temperature provides particles more kinetic energy: increasing rate of diffusion Importance: Gases Necessary for gas exchange Water as the solvent Plants can't obtain minerals unless they are dissolved in water Enzymes & hormones can't be secreted unless they are dissolved in water Examples in Plant Cells Photosynthesis 2diffuses into leaves via the stomata Oxygen produced diffuses out from the leaves via stomata Example in Animal Cells Gas Exchange Oxygen diffuses from the lungs (high concentration) & into the blood (low concentration) 2diffuses out of blood capillaries & into the lungs

B2.02 Osmosis Net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane (Specialised form of diffusion): Diffusion of water across a partially permeable membrane (eg.Visking tube/cell membrane) Importance: Plants only transpire by osmosis Water from soil diffuses into root hair cells Diffuses across cortex cells & into xylem vessels & taken up the leaf Diffuses across the mesophyll cells & out of the stomata In Plant Cells

 Do not burst in pure water Will take in water by osmosis through its cell membrane

Water goes in the cytoplasm & vacuole will swell (turgid) Cell wall stops the cell from bursting; restricts efforts of cytoplasm to move out If there is a lower water concentration outside the plant, cell water will move out of the cell until the concentrations are equal If the concentration gradient is too high, the cell membrane will move away from the

cell wall (plasmolysis) Cell will become flaccid; plant will wilt

In Animal Cells Bursts in pure water Absorbs water by osmosis; if concentration gradient is too high, cell will burst If there is a lower water concentration outside the cell, water will move out until the concentrations are equal If the concentration gradient is too high, the cell will shrivel

B3: Biological Molecules B3.01 Water Functions Main component of living organisms Inorganic biological molecules 70% of the human body weight Medium for metabolic reactions to take place in an organism Metabolism: Chemical reactions that take place inside the body Solvents for most substances Regulation of body temperature Transporting of dissolved substances Digested food & oxygen must be dissolved in water found in blood before being transported Waste products (eg. ) need to be dissolved in water found in blood to be

2

transported away Organisms will die if they do not have enough water B3.02 Carbohydrates Made up of carbon, hydrogen & oxygen Organic biological molecule Sugars Sweet; soluble in water Used during respiration to provide energy Monosaccharides (single sugars)

Small molecules that can't be digested (broken down) into simpler substances Small enough to diffuse across cell membranes into the cells

Eg. Glucose, Fructose, Galactose (6126 ) Disaccharides (double sugars)

Made up of two molecules of monosaccharides that are chemically bonded together

Eg.

Maltose,

sucrose,

lactose

(

12 22 11

)

Polysaccharides

Complex carbohydrates made up of many monosaccharides chemically bonded together

Insoluble in water; not sweet

Eg. Cellulose, starch, glycogen

Polysaccharid Structure

Function

Occurrence

e

Starch

Thousands of glucose molecules chemically bonded together

In Plants Stores starch; easy to change to glucose (vice versa) Some plants store large quantities of starch in their seeds

In Animals Don't store starch; store carbohydrates in the form of glycogen

Plants Storage organs of plants

Glycogen

Thousands of glucose molecules chemically bonded together but is more highly branched than starch

In Animals Stored in small quantities Used for storage of energy

Animals Stored in the liver & muscle s

Cellulose

Thousands of glucose molecules (different from that of starch) chemically bonded together

In Plants Used to make plant cell wall

In Animals Can't be digested by humans so serves as a dietary fibre to prevent constipation

Plants Storage organs of plants

Function One gram of carbohydrates releases 17KJ; (energy released by respiration) Respiration (glucose) Animals Form in which carbohydrates are transported around the body Plasma contains dissolved glucose (cells use to carry out chemical activities) Plants Uses glucose in respiration to provide energy but does not transport it Transport sucrose; cells change sucrose to glucose when they need to use it

Testing Benedict's test for carbohydrates Iodine test for starch

B3.03 Fats (Lipids) Made up of carbon, hydrogen & oxygen Lower oxygen:hydrogen ratio compared to carbohydrate molecules Organic biological molecule Made of 4 smaller molecules joined together 1 glycerol molecule + 3 fatty acid molecules No general formula for fats Insoluble in water Fats at room temperature = oils Functions Source of energy & used to store food A material to insulate animals from excessive heat loss Protection from damage for vital organs Solvent to dissolve fat-soluble vitamins Essential part of cell membranes

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download