Biology Prelim Notes PDF

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Biology Prelim Notes   

Cells as a Basis of Life Cell Structure - WHAT Distinguishes One Cell from Another? Syllabus Dot Point: -

Investigate different cellular structures including but not limited to; Examining a variety of prokaryotic and eukaryotic cells Describe a range of technologies that are used to determine a cell’s structure and function

Notes: Cell Theory: - All organisms are made up of cells. - New cells are produced from existing cells. - A cell is the smallest unit within a living thing. Types of Cells: - Prokaryotic; ↳ They are the simplest cells which do not have a membrane-bound nucleus. ↳ There are two types; ○ Bacteria ○ Archaea ↳ DNA is in a circular loop called a plasmid. ↳ Typically unicellular. - Eukaryotic; ↳ Are larger and more complex than prokaryotic cells. ↳ Possess a membrane-bound nucleus which stores genetic information. ↳ They have membrane-bound organelles which work together to undergo biochemical processes such as respiration and photosynthesis. ↳ Linear DNA is held in the nucleus. ↳ Usually multicellular. ↳ Animal and plant cells are eukaryotic.

Technologies: - Light Microscopes; ↳ The light source passes through a condenser lens and then through the specimen which then beams through the convex objective lens, where the image is magnified and viewed through the ocular lens. ↳ Can produce magnifications of up to 2000x and resolution of 200nm. ↳ Living and non-living objects can be viewed in a light microscope.

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Investigate a variety of prokaryotic and eukaryotic cell structures, including

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Fluorescence Microscopes; ↳ It is similar to light microscopes however you are able to produce images of specific parts of cells. ↳ The sample viewed is labelled as the fluorescent substance. ↳ The sample is illuminated with a high-intensity source of light resulting in the fluorescent substance emitting light. ↳ The light is directed through filters which separate it from surrounding light so the viewer can only see the areas of the sample that is fluorescing.

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Electron Microscopes; ↳ The electron microscopes display structures at both cellular and subcellular levels. ↳ These microscopes use electron beams and electromagnets. ↳ Two types; ○ Transmission Electron Microscope (TEM) ➢ The electrons are passed through the specimen to produce a 2D image. ➢ Can magnify up to an 1 500 000x and has a resolution of 2nm. ○ Scanning Electron Microscope (SEM) ➢ It bombards solid specimens with a beam of electrons which results in the secondary electrons to be emitted from the surface layers of the specimen. ➢ It has a poor resolution of about 10nm however it is able to produce 3D images of surfaces.

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Confocal Laser Scanning Microscopes; ↳ They use pinpoint laser beams to make an image of the sample at different levels which are combined to create a 3D image of the sample.

Sizes of Cells: 1 metre (m) = 100 centimetres = 1000 millimetres

= 1 000 000 micrometres but not limited to; Scaled = 1 000 000 000 nanometres diagrams of a Organelles in Cells: variety of cells Comparing and Organelle Plant/Animal? contrasting different cell Cell Membrane Both organelles and arrangements Modelling the structure and function of the Cell Wall Plant fluid mosaic model of the cell membrane Centriole Animal

Function A thin membrane which surrounds the cell wall and filters what can enter and exit the cell. It gives the cell its shape which is thicker and more frigid. A dense, granular structure that has two centrioles that play an important role in cell division and informing the spindle.

Chloroplast

Plant

Conducts photosynthesis

Cytoplasm

Both

A fluid that contains all organelles and supports them.

Cytoskeleton

Both

Helps maintain shape, move and shift things around and inside the cell.

Golgi Body

Both

Responsible for directing molecular traffic in the cell; modifies, sorts and transfers molecules.

Lysosomes

Animal

Contains enzymes that digest waste and “clean up” the cell.

Mitochondria

Both

Converts chemical energy from food into compounds more convenient for the cells to use.

Nucleus

Both

Directs the activity of

the cell and stores DNA Plasma Membrane

Both

Protoplasm

The outer part of the cell which allows things inside and outside of the cell. The living content of a cell that is surrounded by the cell membrane

Rough Endoplasmic Reticulum (RER)

Both

Responsible for synthesis and transport of proteins.

Smooth Endoplasmic Reticulum (SER)

Both

Makes sex hormones, lipids and enzymes

Vacuole

Plant

Stores nutrients and water

The Fluid Mosaic Model: - The cell membrane is selectively permeable and performs the function of controlling the movement of substances into and out of the cell. - The currently accepted model of the structure of the cell membrane is the fluid mosaic model. ↳ It depicts a ‘fluid’ phospholipid bilayer with different types of proteins embedded in it, creating a ‘mosaic’ effect. ↳ Some membrane proteins form pores (temporary or permanent), some form of active carrier systems or channels for transport and others (glycoproteins) have carbohydrates attached for cell recognition.

Cell Function - How do Cells Coordinate Activities within their Internal Environment and the External Environment? Syllabus Dot Point: -

Notes:

Investigate the way in Movement of Materials in and out of Cells: which materials can - Substances move from the internal environment of the cell to the external environment (and vice versa) by passing across the cell move into and out of cells, including but not membrane. - The cell membrane is selectively permeable and controls the movement limited to; Conducting a of substances into and out of the cell. - Gases, nutrients, water and ions are required by the cell, while wastes practical investigation and cellular products need to be removed from the cell. - The permeability of a membrane to a particular molecule depends on its modelling diffusion and size, electrical charge and its lipid solubility. - Plant cells walls are permeable to most substances. osmosis. Examining the cc roles of active Diffusion: transport, - It is the movement of particles from a region of high concentration to a region of low concentration until equilibrium is reached. endocytosis, - At equilibrium, there is no net movement of particles in either direction. and exocytosis. - Does not require the input of energy (passive transport). Relating to the - It occurs faster with a higher temperature or a steeper concentration exchange of gradient. materials - Small, uncharged molecules such as oxygen and carbon dioxide will across diffuse easily across the cell membrane. membranes to - Facilitated diffusion allows larger molecules and small electrically the charged ions to diffuse across the cell membrane aided by carrier or surface-area-to channel proteins. -volume ratio - Factors Affecting Diffusion concentration 1. Concentration Gradient  → the rate of diffusion will be higher gradients and when there is a greater difference characteristics 2. Distance  → diffusion over a shorter distance occurs at a greater of the materials rate compared to a larger distance being 3. Surface Area → diffusion rates are greater when there is a larger exchanged. surface area 4. Physical Barrier → Thick barriers slow down the rate of diffusion while a thinner barrier enhances the rate  A higher temperature causes particles to have a 5. Temperature → higher rate of diffusion until a certain point where they will denature Osmosis: - It is the process by which water moves from an area of low concentration of water to an area of high concentration of water through a selectively permeable membrane. - It requires no energy input → passive transport - The more water that moves across the membrane, the higher osmotic pressure created.

Active Transport: - It is the movement of molecules from a region of low concentration to an area of high concentration. - It moves against the concentration gradient and requires the input of energy. Endocytosis: - It moves large molecules that cannot cross the cell membrane into a cell. - Requires the expenditure of energy. - The cell membrane changes shape and surrounds and engulfs the particle so that it enters the cell. → - Phagocytosis; ↳ Process whereby solid particles are engulfed by the cell membrane - Pinocytosis; ↳ The engulfing of fluid substances by the cell membrane. Exocytosis: - Involves a membrane-bound vesicle moving to the cell membrane, fusing with it and then releasing its contents to the exterior of the cell. Factors Affecting the Exchange of Materials Across Membranes: - Chemical factors; ↳ The chemical properties of a substance affect its transport across cell membranes, uncharged molecules can easily penetrate the cell membrane as they can dissolve through the phospholipid bilayer. - Physical factors; ↳ The size and shape of the molecule affects its ability to move across the cell membrane. Small molecules are able to easily diffuse between the phospholipids, however, very large molecules need to be transported via endocytosis or exocytosis. - Concentration gradient; ↳ The relative concentration of the substance on either side of the membrane affects the rate of diffusion of that substance. ↳ If the concentration gradient is high, the substance will diffuse rapidly. ↳ If the concentration gradient decreases, the rate of diffusion will be slower. ↳ When the concentration gradient reaches equilibrium, there will be no net movement across the cell membrane. Surface-Area-to-Volume Ratio: - It is calculated by finding the total area of the surface of the shape. - Volume is the total space that a shape takes up. - SA: V is calculated by dividing the surface area of an object by its volume. - The SA: V ratio of a cell will determine how efficiently substances move into and out of a cell. - A high SA: V allows the most efficient movement of substances into

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Investigate cell requirements, including but not limited to: Suitable forms of energy, including light energy and chemical energy in complex molecules Matter, including gases, simple nutrients, and ions. Removal of wastes

Cell Requirements: - Cells require organic and inorganic nutrients. - They are utilised in the following ways; ↳ Essential building blocks from which cells and living tissues are made. ↳ As a source of stored energy for the cell. -

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Investigate the biochemical processes of photosynthesis, cell respiration and the removal of cellular products and wastes in eukaryotic cells

and out of the cell. Large cells have a low SA: V, small cells have a large SA: V. Long, flat cells have a higher SA: V than a spherical cell with the same volume.

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The four main groups of biomacromolecules are carbohydrates, proteins, lipids and nucleic acid. They are made up of carbon, hydrogen and oxygen atoms, but they are in different proportions. Autotrophic organisms can build their own organic compounds, whereas consumer organisms must make their own organic compounds from their food. Carbohydrates can be used as a source of energy, for storage of energy and sometimes as a structural component of the cell. Lipids are used for energy storage, structural parts of membranes and components of hormones. Proteins have structural roles in cells and tissues. Proteins such as enzymes also have a functional role. The two types of nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA contains chemical information that controls the cell activities and the production of proteins, RNA assists in the manufacture of the proteins. The energy in cells is transported within cells by small and mobile ATP molecules. ATP stores energy in a high-energy bond that attaches the third phosphate group to the ADP molecule. When energy is required, the high-energy bond is broken, releasing energy, a phosphate group and ADP.

Photosynthesis: - It is the process where plants use light energy, trapped by chlorophyll, to break down water and carbon dioxide molecules, and build them up into oxygen, glucose and water molecules. Light energy Carbon dioxide + water ------------------- → glucose + oxygen Chlorophyll -

It is a series of smaller reactions occurring across two stages. The light-dependent stage occurs in the grana where light splits the

water molecules into oxygen and hydrogen. - The light-independent stage occurs in the stroma where carbon dioxide and hydrogen combine to form glucose. Aerobic Cellular Respiration: - When glucose and oxygen combine, energy is produced along with water and carbon dioxide. This process is made up of many reactions. Glucose + oxygen (+ADP+P) many chemical reactions →  carbon dioxide + water + energy (ATP) -

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The energy produced is stored in ATP molecules. The first step of this process occurs in the cytoplasm and is called glycolysis. In this step, one glucose molecule is broken down into two pyruvate molecules and two ATP. The second step in the reaction occurs in the mitochondria where pyruvate, in the presence of oxygen (aerobic cellular respiration), is broken down to release carbon dioxide, water and 34 ATP.

Anaerobic Cellular Respiration: - Anaerobic (without oxygen) cellular respiration produces ethanol and carbon dioxide in bacteria, yeast and plant cells, and lactic acid in animal cells. Two ATP molecules are produced in this process for the respiration of each molecule of glucose. - Wastes are the products of cellular reactions that are not required. - Many of these wastes can be removed by simple diffusion through the cell membrane. - Other wastes can be removed by exocytosis or destroyed by the enzymes present in lysosomes. -

Investigate the effects of the environment on enzyme activity through the collection of primary or secondary data

Enzymes: - They are the proteins that control cellular reactions. ↳ Cellular products and wastes must be removed from the cell to maintain efficient cell functioning. - In enzyme-catalysed reactions, the substrate attaches to the shape on the surface of the enzyme (the active site) and forms a substrate-enzyme complex. - The reaction then occurs and the products are released. The enzyme can be re-used for the same reaction. - There are two models of enzyme action → the lock-and-key model and the induced-fit model. Factors Affecting Enzyme Activity: - Temperature; ↳ The activity of the enzyme increases as temperature increases until the optimal temperature is reached. With further temperature increases, the enzyme activity decreases and then stops completely when the high temperatures destroy (denature) the structure of the enzyme. - pH levels; ↳ Each enzyme has an optimum pH at which it functions most

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efficiently. Substrate Concentration; ↳ As the substrate concentration increases, the activity of the enzyme increases until all the enzymes are saturated. After this, further increases in substrate concentration will not lead to increases in enzyme activity.

Organisation of Living Things Organisation of Cells-How are Cells Arranged in a Multicellular Organism? Syllabus Dot Point: -

Compare the differences between unicellular, colonial and multicellular organisms by: Investigating structures at the level of the cell and organelle Relating structure of cells and cell specialisation to function

Notes: -

Organisms can exist as a single cell (unicellular), single cells working together (colonial) or as an organism made up of many cells (multicellular), however, they all have similarities; ↳ They are all composed of cells ↳ These cells all possess cell membranes, cytosol, ribosomes and some sort of genetic material.

Unicellular Organisms: - They contain only one cell which can either be prokaryotic or eukaryotic. - A single cell is responsible for all of its own life processes. - Prokaryotic cells have no membrane-bound nucleus or organelles, however, their simple structures limit the number of reactions that they can carry out. - Cells of unicellular organisms have a highSA: V, which allows efficient movement of substances into and out of the cell. Colonial Organisms: - They are thought the be the evolutionary link between unicellular and multicellular organisms. - They are composed of individual cells living together in a colony. - All cells in the colony are capable of carrying out all of the metabolic functions necessary for life, however, simple specialised cells can be present in the colony to improve the efficient functioning of the organism. Multicellular Organisms:

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They are composed of many different types of specialised cells. Similar specialised cells are grouped together and perform specific functions that combine for the efficient functioning of the organism. Individual cells cannot live independently of each other.

Specialised Cells: - Stem cells are undifferentiated cells with no specialised structure or function. - Specialised cells are formed when differentiation of the stem cells occurs and they develop suitable structural features that allow them to carry out their specific functions. - They type of cell that is formed is determined by the location of the undifferentiated cells in the organism and the particular genes that are switched on. - Stem cells can either be embryonic or adult stem cells. - In plants, specialised cells are formed by the differentiation of meristematic tissue. Relationships between Cell Structure and Function: - The cells of those parts of the body involved in exchanging substances with the environment have special structural features to increase their SA: V, allowing them to exchange the required materials more efficiently. - The cell structure is related to the particular function of the specialised cell. - Some cells may flatten and become longer to increase the SA: V or have many folds to increase surface area. E.g. root hair cells - Another example is the red blood cells that are very small and have a particular shape to increase SA: V for the exchange of oxygen. They lack a nucleus and organelles, enabling more haemoglobin to be carried in the cell. -

Investigate the structure and function of tissues, organs and systems and relate those functions to cell differentiation and specialisation

Animal Tissues: - Epithelial Tissue; ↳ It is a tissue that covers body surfaces, protects organs and forms glands. ↳ The cells are densely packed and can occur in either single sheets or layers. ↳ Does not contain blood vessels and relies on the underlying connective tissue for nutrients. ↳ Skin, the surface of organs of the digestive system, respiratory system and other organs. ↳ The cells are organised very close to each other, aiding their role as barriers to injury and infection. ↳ They may also be specialised for absorption or secretion. - Connective Tissue; ↳ It varies greatly in the form it takes and its function. ↳ They all share the common characteristic of an extracellular matrix with cells scattered through it. ↳ This matrix is made up of protein fibres collagen (strength) and

elastin (flexibility). It provides support and ensures that different parts of the body are bound together and protects against damage. ↳ The different types vary in their density and the way their cells are specialised. ↳ There are numerous types including fibrous connective tissue, loose connective tissue, adipose tissue and cartilage, each of which differ due to their arrangement of cells and their spec...