Qcaa biology unit 1 compiled notes 2020 PDF

Preview

Summary

QCAA...

Description

BIOLOGY UNIT 1 CELLS AND MULTICELLULAR ORGANISMS

TOPIC 1: Cells as the Basis of Life Prokaryotic and Eukaryotic Cells 1.1.2 a-f Recognise the requirements of all cells for survival, including • • • • •

energy sources (light or chemical) matter (gases such as carbon dioxide and oxygen) simple nutrients in the form of monosaccharides, disaccharides, polysaccharides amino acids, fatty acids, glycerol, nucleic acids, ions and water removal of wastes (carbon dioxide, oxygen, urea, ammonia, uric acid, water, ions, metabolic heat).

Recognise that prokaryotic and eukaryotic cells have many features in common, which is a reflection of their common evolutionary past. Recall that prokaryotic cells lack internal membrane bound organelles, do not have a nucleus, are significantly smaller than eukaryotes, usually have a single circular chromosome and exist as single cells. Understand that eukaryotic cells have specialised organelles to facilitate biochemical processes. Photosynthesis (chloroplasts) Cellular respiration (mitochondria) Synthesis of complex molecules including proteins (rough endoplasmic reticulum), carbohydrates, lipids and steroids (smooth endoplasmic reticulum), pigments, tannins and polyphenols (plastids) The removal of cellular products and wastes (lysosomes) Identify the following structures from an electron micrograph: chloroplast, mitochondria, rough endoplasmic reticulum and lysosome. Compare the structure of prokaryotes and eukaryotes.

Requirements for Cell Survival All cells require basic needs to survive. i. •

Energy sources: Can be light or chemical. i.e ATP via glucose

ii. Matter: • Includes 𝐻2 𝑂, 𝐶𝑂2 , 𝑂2 , nitrates, phosphates, and inorganic compounds. • Organic molecules. iii. Simple nutrients: • Monosaccharides: carbohydrate monomers i.e simple sugars.

• •

Disaccharides: formed from 2 monosaccharides; forms glycosidic bond e.g sucrose. Polysaccharides: formed by the addition of monosaccharides by condensation reactions e.g starch, glycogen.

iv. Lipids: • Ester of fatty acids and glycerol.

v. Proteins: • Macromolecule consisting of 1 or more polypeptide chains. • Formed by the condensation of amino acids.

vi. Nucleic acids: • Macromolecules that make up genetic material (rNA and DNA) • Built up by nucleotides, each consists of - A pentose sugar (5C) arranged in a ring. - Organic nitrogen base. - A phosphate group.

vii. Waste removal: • Via lysosomes • Wastes include: - Urea - Ammonia - Uric acid - 𝐻2 𝑂 - 𝐶𝑂2 - 𝑂2

Eukaryotic Cells Eukaryotic cells have specialised cells to facilitate biochemical processes. i. • •

Chloroplast Site of photosynthesis. Absorb sunlight and uses 𝐻2 𝑂 and 𝐶𝑂2 to produce glucose, oxygen and water.

Photosynthesis Reaction 12𝐻2 𝑂 + 6𝐶𝑂2 → 𝐶6 𝐻12 𝑂6 + 6𝑂2 + 6𝐻2 𝑂 ii. Mitochondria • Site of cellular respiration • Produces ATP (adenosine triphosphate)

Cellular Respiration Reaction Note: it is the opposite reaction to photosynthesis. 𝐶6 𝐻12𝑂6 + 6𝑂2 → 6𝐻2 𝑂 + 6𝐶𝑂2 + 36 − 38 𝐴𝑇𝑃

iii. Rough Endoplasmic Reticulum • Site of synthesis of complex molecules i.e proteins.

iv. Smooth Endoplasmic Reticulum • Site of synthesis of carbohydrates, lipids, and steroids.

v. Plastids • Synthesis of pigments, tannins, and polyphenols.

vi. Lysosomes • Removal of cellular products and wastes.

Prokaryotic vs Eukaryotic Cell Prokaryotic Cell • Most are simple organisms. • Simple structure i.e no membrane. • • •

Bound organelles No nucleus Single circular chromosome.

Both •

Have DNA - Cell membrane - Cell wall - Ribosomes - Cytoplasm

Eukaryotic Cell • Part of multicellular organisms • Specialised organelles - Chloroplast - Mitochondria - Rough/Smooth Endoplasmic Reticulum

Cell Membrane 1.1.1 a-g Describe the structure of the cell membrane (including protein channels, phospholipids, cholesterol and glycoproteins) based on the fluid mosaic phospholipid bilayer model. Describe how the cell membrane maintains relatively stable internal conditions via the passive movement (diffusion, osmosis) of some substances along a concentration gradient. Explain how the cell membrane maintains relatively stable internal conditions via the process of active transport of a named substance against a concentration gradient..

Understand that endocytosis is a form of active transport that usually moves large polar molecules that cannot pass through the hydrophobic cell membrane into the cell. Recognise that phagocytosis is a form of endocytosis. Predict the direction of movement of materials across cell membranes based on factors such as concentration, physical and chemical nature of the materials. Explain how the size of a cell is limited by the relationship between surface area to volume ratio and the rate of diffusion.

Cell membranes have multiple functions: 1. Acts as a semi-permeable barrier for waste and nourishment. 2. Sire of passive and active transport.

The cell membrane is commonly described as the Fluid Mosaic Model • •

Fluid: able to move; flexible. Mosaic: made up of many components.

Components of Cell Membrane i. • • •

ii.

Phospholipid: Hydrophilic head Hydrophobic tail Make up the bilayer.

Proteins

•

Integral proteins: - Embedded in bilayer - Control movement of specific molecules in/out of cell i.e protein channel.

•

Peripheral proteins: - Embedded in bilayer - Direct and maintain intracellular cytoskeleton.

•

Glycoprotein: - Attached to carbon chain. Has a role in: - Cellular recognition - Immune responses - Stabilise membrane structure.

iii. Cholesterol • Positioned between phospholipids • Disturbs packaging of hydro-carbons tails to maintain fluidity of cell membrane.

Transport Across Membranes The cell membrane maintains stable internal conditions via two types of transports across the membrane. 1. Active transport 2. Passive transport Passive Transport

Osmosis

Active Transport

Diffusion

Simple

Facilitated

Active Transport • Requires energy • Moves against the concentration gradient or an ionic gradient.

Active transport of materials out of a cell is exocytosis; by fusion of a vesicle by cell membrane. Active transport of material into a cell is endocytosis. Endocytosis pathways can be subdivided into several categories: i. -

ii. -

Phagocytosis Receptor mediated capture of large particles such as bacteria. i.e cell eating. Pinocytosis Formation of large intracellular vesicles filled with extracurricular material. i.e cell drinking - occurs by unfolding cell membrane to form a channel.

Passive Transport • Requires no energy. • Moves with concentration gradient. Diffusion is a process where molecules or ions of liquids and gases tend to spread out from regions of higher concentration to regions of lower concentrations.

i.e molecules tend to seek even distribution. There are three main factors that affect rate of diffusion. 1. Temperature: molecules move faster at higher temperatures. 2. Particle size: small molecules require less energy to move. 3. Concentration: the greater the difference in concentration between two locations, the faster the diffusion will occur. There are two methods of diffusion: 1. Simple 2. Facilitated

1. Simple Diffusion • Free of unaided movement of molecules or ions though cell membrane from an area of high concentration to an area of low concentration.

Dynamic Equilibrium: state of balance that exists when the amount of a particular substance entering the cell is equal to the amount leaving it.

2. • • •

Facilitated Diffusion Aided by a protein Molecules are carried across membrane by globular proteins. No overall energy is expended in the process.

Osmosis • Occurs when there is a concentration gradient of solute across a membrane which is impermeable to the solute. • Moves from an area of low solute concentration to an area of high solute concentration.

Osmotic potential: capacity of a solution to lose water molecules through a semi-permeable membrane. •

Depends on concentration of solute in solution (e.g cell cytoplasm) compared with concentration on other side of membrane (e.g extracellular fluid).

Hypertonic Extracellular Fluid • •

Extracellular fluid has higher solute concentration than cytoplasm. As such the osmotic potential is low. Water moves out of the cell.

Hypotonic Extracellular Fluid • •

Extracellular fluid has lower solute concentration than cytoplasm. As such, the osmotic potential is high. Water moves into the cell.

In plant cells, the membrane shrinks away from the cell wall when placed in a hypertonic solution. If cells are then placed in a hypotonic solution, water enters the cell, restoring it back to its normal state.

A similar phenomenon occurs in animal cells. When placed in hypertonic solutions, the entire cell shrinks. In hypotonic solutions, the cell expands, stretching the membrane which may burst.

Energy and Metabolism 1.1.5 a-h Recall that organisms obtain the energy needed to recycle Adenosine Triphosphate (ATP) from glucose molecules in the process of cellular respiration Recall that the process of photosynthesis is an enzyme-controlled series of chemical reactions that occurs in the chloroplast in plant cells and uses light energy to synthesise organic compounds (glucose), and the overall process can be summarised in a balanced chemical equation carbon dioxide + water glucose + oxygen + water 12𝐻2 𝑂 + 6𝐶𝑂2 → 𝐶6 𝐻12 𝑂6 + 6𝑂2 + 6𝐻2 𝑂

Summarise the process of photosynthesis in terms of the light-dependent reactions and light-independent reactions. Demonstrate the relationship between the light-dependent reactions and light-independent reactions. Recognise that cellular respiration is an enzyme-controlled series of chemical reactions and that the reaction sequence known as aerobic respiration (glycolysis, Krebs cycle and electron transfer chain) requires oxygen. Summarise the reactions of aerobic respiration by the chemical equation. glucose + oxygen carbon dioxide + water + energy 𝐶6 𝐻12𝑂6 + 6𝑂2 → 6𝐻2 𝑂 + 6𝐶𝑂2 + 36 − 38 𝐴𝑇𝑃 Recall that, with an undersupply of oxygen, ATP is produced from glucose by the reaction sequence known as anaerobic respiration (glycolysis with ‘fermentation’). Analyse multiple modes (i.e. diagrams, schematics, images) of energy transfer.

Organisms obtain the energy needed to recycle ATP from glucose molecules in the process of cellular respiration. Cellular respiration is an enzyme-controlled series of chemical reactions represented by the equation: 𝐶6 𝐻12𝑂6 + 6𝑂2 → 6𝐻2 𝑂 + 6𝐶𝑂2 + 36 − 38 𝐴𝑇𝑃 Cellular respiration (also known as aerobic respiration) requires oxygen and is completed in four stages: 1. Glycolysis 2. Kreb’s Cycle 3. Oxidative Phosphorylation i. Electron transport chain ii. Chemiosmosis

1. Glycolysis • Can occur with or without oxygen. i. In presence of oxygen - It is the first stage of all cell respiration. ii. Without oxygen - Glycolysis makes small amount of ATP i.e fermentation (anaerobic respiration). • Takes place in the cytoplasm. Glucose (a 6 carbon molecule) is split into 2 molecules i.e 3 carbon sugars. The following is produced: - Net production of 2 ATP - 2 molecules of Pyruvic Acid - 2 ‘high energy’, ‘electron carrier’ molecules of NADH.

2. Kreb’s Cycle • Pyruvate are converted to acetyl CoA. • ‘electron carriers’ (NAD and FAD) are produced with 2 ATP molecules. - NAD and FAD are reduced, becoming NADH and FADH2. - NADH and FADH2 carry ‘high energy electrons’ to the next stage.

• •

Kreb’s Cycle only occurs when oxygen is present but doesn’t use it directly. - It occurs in the matrix of the mitochondria. The process yields: - 6CO2 - 8 NADH and 2FADH2 (electron carriers) - 2 ATP

3. Oxidative Phosphorylation i. Electron transport chain • Requires oxygen directly as the final electron receptor. • Series of electron carriers in the membrane of the mitochondria in eukaryotic cells. • ‘high energy’ electrons are passed to oxygen. - A H+ gradient is formed outside inner membrane.

•

ii. Chemiosmosis Enzyme ATP synthase uses energy produced by pressure of high concentration of protons outside membrane to drive production of ATP from ADP. - 34 ATP molecules are produced.

Photosynthesis Photosynthesis is also an enzyme-controlled series of chemical reactions represented by the equation: 12𝐻2 𝑂 + 6𝐶𝑂2 → 𝐶6 𝐻12 𝑂6 + 6𝑂2 + 6𝐻2 𝑂 Note: it is the opposite of cellular respiration. During photosynthesis: •

Light energy is converted into chemical energy.

Process of photosynthesis: i. • • • •

• •

Light dependent reactions Take place in pigment systems of the thylakoid sacs of the chloroplast. Chloroplast pigment absorbs light energy. This energy ‘excites’ electrons in the chlorophyl molecules, causing their release from the molecule. Energy of the excited molecules is used: - In the formation of 18 ATP molecules. - To decompose 12 H2O molecules into 24 hydrogen atoms and 6 oxygen gas molecules. Hydrogen atoms are taken up by a hydrogen acceptor and the oxygen is released as a metabolic waste product (into the environment). The electrons are returned to chlorophyll molecules.

ii. Light independent reactions • Occurs in stomata. • Needs the products of light dependent reactions. • CO2 is reduced by hydrogen atoms formed in light dependent reactions with the input of energy from ATP to form glucose. • This series of reactions is known as the Calvin-Benson Cycle.

Internal Membranes and Enzymes 1.1.4 a-d Explain, using an example, how the arrangement of internal membranes can control biochemical processes (e.g. folding of membrane in mitochondria increases the surface area for enzyme-controlled reactions). Recognise that biochemical processes are controlled and regulated by a series of specific enzymes.

Describe the structure and role of the active site of an enzyme. Explain how reaction rates of enzymes can be affected by factors, including temperature, pH, the presence of inhibitors, and the concentrations of reactants and products.

Enzymes are globular proteins that lower the activation energy needed for a chemical reaction to take place.

Reaction rate of enzymes can be affected by factors: i. •

Temperature The higher the kinetic energy as a result of higher temperature, the higher the amount of successful collisions.

ii. pH • Optimum pH levels vary between enzymes. iii. Presence of Inhibitors • Alters catalytic action. iv. Concentration • Decreased space between molecules as a result of higher concentrations allow for more successful collisions.

Induced Fit The Induced Fit hypothesis suggests that the enzyme’s function depends on the shape. •

The enzyme attaches to a substrate. - Their shapes are complementary.

-

Forms enzyme-substrate complex when activated into forming products. Product molecules no longer fit into active site and escae into surrounding medium.

Internal Membrane •

Increased surface area to volume ratio increases reaction’s ability to take place.

e.g cristae of mitochondria •

Folding of inner membrane increases surface area for enzyme-controlled reactions.

TOPIC 2: Multicellular Organisms Cell Differentiation and Specialisation 1.2.1 a-c Understand that stem cells differ from other cells by being unspecialised and have properties of self-renewal and potency. Recognise that stem cells differentiate into specialised cells to form tissues and organs in multicellular organisms. Recognise that multicellular organisms have a hierarchical structural organisation of cells, tissues, organs and systems.

Multicellular Organisms Multicellular organisms have a hierarchical structural organisation of cells.

A long series of organisation is undertaken to produce the final organism. 1. 2. 3. 4.

Cell must produce many more cells with the same genetic code. Cells must specialsie their structure and function Cells must be able to coordinate (i.e communicate) Cells forming organism must be located near cells that support them.

Stem Cells Stem cells are unspecialised cells that have the capacity to develop into many different cell types under special conditions. All stem-cells have two properties: 1. Self-renewal: • The ability to go through several cell cycles without further differentiation. 2. Potency: • The ability to differentiate into specialised cell types.

Gas Exchange and Transport 1.2.2 a-c Explain the relationship between the structural features (large surface area, moist, one or two cells thick and surrounded by an extensive capillary system) and function of gaseous exchange surfaces (alveoli and gills) in terms of exchange of gases (oxygen, carbon dioxide) Explain how the structure and function of capillaries facilitates the exchange of materials (water, oxygen, carbon dioxide, ions and nutrients) between the internal environment and cells Use data presented as diagrams, schematics and tables to predict the direction in which materials will be exchanged between -

alveoli and capillaries capillaries and muscle tissues.

Gas Exchange

i. •

Stomata Small pores on underside of leaf.

ii. Guard cells • Can open and close the stomata. • When plant is full of water, guard cells become turgid, opening the stomata. • When plan is dehydrated, guard cells close stomata to retain water.

Through the stomata and the guard cells, gases like carbon dioxide, oxygen gas, and water vapour are able to move throughout the plant.

Leaf Diagram

i. • •

Petiole Xylem transports water and ions from roots Phloem transports sugars and other small organic molecules between different parts of the plant....