preliminary biology - synergyhsc.com · notes preliminary biology module 1: cells as the basis of...

Preliminary Biology Notes

Module 1: Cells as the Basis of Life

Part 1 of 2

Brought to you by Jemma Lang from:

Cells as the Basis of Life Synergy Education

Written by HSC Synergy Education 2018 for every HSC Chemistry student out there! Every part of this publication may be reproduced,

stored in a retrieval system, transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise as it is

FREE to use for your benefit! ☺

2

1. Cellular Structure Inquiry question: What distinguishes one cell from another?

Prokaryotes:

• Prokaryotes are a basic type of cell, characterised by the presence or absence of particular organelles

• Prokaryotes lack internal membrane-bound organelles, do not have a defined nucleus, are significantly smaller than eukaryotes, and exist as unicellular organisms.

• They emerged around 3.5 billion years ago, and are considered to be the first “actual” cells

- Bacteria and archaea are prokaryotic cells - These cells are typically 0.1 – 1 µm in size

• 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





3

Eukaryotes:

• Eukaryotes are a more complex cell type, containing membrane-bound organelles, and a membrane-bound nucleus.

- These cells include plant and animal cells and fungi cells - Eukaryotic cells are typically 7 – 100 µm in size - Eukaryotic cells can be unicellular, colonial, or multicellular

Structures in a Cell:

Structure Description Function

Cell Wall

Prokaryotic and Eukaryotic

• Rigid, outer layer of the cell • Semi-permeable • Composed of polysaccharides such

as cellulose

Provide structure and shape Protection due to the rigid layer

Capsule

Prokaryotic

• Found in only some bacterial cells • Very outer layer of the cell • Semi-Permeable

Additional protection Assists retaining moisture Helps cell adhere to surfaces

Cytoplasm


• Gel-like substance • Composed mostly of water and

dissolved substances, e.g. salts, enzymes, organic molecules

Gives cell shape & maintain turgidity Suspends all organelles and parts Chemical reactions involved with cellular respiration occur here





4

Cell

Membrane/Plasma Membrane


• Surrounds the cell’s cytoplasm • Selectively permeable • Composed of primarily lipids

Regulates the flow of substances into and out of the cell Separates the inside of the cell from the outside environment, and it is responsible for intercellular communication

Pili/ Pilius (singular) Prokaryotic

• Hair-like structures • Protrude from the cell • Range in length • Very adhesive

Allows the cell to attach to surfaces or other bacteria

Flagella

Prokaryotic and some

Eukaryotic

• Long, whip-like protrusion • Capable of moving quite fast

Aids in locomotion of the cell, which allows it to seek out food, and escape hostile environments

Ribosomes


• Sphere-shaped structure within the cytoplasm

• Composed of RNA and other proteins

Responsible for the manufacturing of proteins

Plasmids Prokaryotic

• Gene-carrying, circular structures • Replicates independently from

chromosomes • Not in every prokaryote • Not membrane-bound

Often, additional genes found in these plasmids provide antibiotic resistance. Can be claimed from other bacterial cells. Make survival of bacterial cells more likely by protecting it from stress-related deaths

Nucleoid Region

Prokaryotic

• Contains single, convoluted strand of DNA

Allows for the replication of the bacterial cell through binary fission





5

Structure Description Function

Golgi Body

Prokaryotic

• An organelle composed of many folded, flattened vacuoles and sacs

• Suspended in the cytoplasm of the cell

• Inc. Golgi apparatus and Golgi vesicles

This organelle is important to the transport and sorting of macromolecules such as proteins and lipids.

Vacuole Eukaryotic

• A membrane-bound cavity within the cell

• Consists of fluid and food or metabolic wastes dissolved in the solution

The organelle is used a storage cavity, allowing the cell to maintain pressure, keep separate wastes and harmful materials and balancing the pH of the cell.

Nucleus

Eukaryotic

• A membrane-bound organelle containing the majority of genetic material

The nucleus is the control centre of the cell, by regulating gene expression. It dictates, by means of DNA, the type and number of molecules synthesized and any chemical reactions within the cell.

Nucleolus Eukaryotic

• A small, round structure within the nucleus. It is not membrane-bound

• rRNA is produced within the nucleolus

The nucleolus is intimately tied to protein production as it produces the RNA that the Ribosome is composed of.





6

Technologies:

• The invention of the light microscope (or compound microscope) allowed the identification of cells as the unit of life!

- The first cell was observed by Robert Hooke in 1665 - Later developments in the light microscope allowed greater resolution (the

ability to distinguish two points of a certain distance apart) lead to greater understanding of cells and their components!

- In 1833 this lead to the formation of the cell theory: an important definition of what a ‘cell’ is:

1. The cell is the unit of structure, physiology, and organization in living things. 2. The cell retains a dual existence as a distinct entity and a building block in the

construction of organisms. 3. Cells form by free-cell formation, similar to the formation of crystals (spontaneous

generation)

- While points one and two are correct, point three is clearly wrong and was amended with “all cells arise from pre-existing cells” by division.

Nuclear membrane Eukaryotic

• The nuclear membrane envelopes the nucleus

• Semi-permeable – contains pores

• Composed of lipids

Responsible for controlling the movement of substances into and out of the nucleus. Protects the nucleus by providing some structure.

Mitochondrion

Eukaryotic

• Small structures consisting of large surface area of folded membrane and a small matrix where fluid is held.

• Mitochondria can combine to make larger ones as needed by the cell

Mitochondria (referred to as the powerhouse of the cell) is responsible for cellular respiration. This occurs on the membrane of the organelle, which explains why mitochondria have a large surface area and why cells may need many mitochondria.





7

• Let’s have a look at how to use the light microscope!

• Some important notes to remember: - The ocular lens is 10X magnification, so if the objective lens is 40X the total

magnification = 10*40 = 400X - Slides are thin glass or plastic rectangles upon which the specimen is

mounted - Wet mounts are most often used to examine live specimens (to ensure they

do not dehydrate) - Cover slips helps to ensure the specimen is flat and thin, and has no air gaps

that could disrupt the image

• The next important technology in determining a cell’s structure and function is the electron microscope

- Electron microscopes were developed in the 1930s and are expensive and difficult equipment to use, requiring training and a scientific laboratory

- The electron microscope works by firing a stream of electrons at the specimen which are deflected onto a fluorescent screen and analysed by a computer to form an image

- Electron microscopes allow investigations at a sub-cellular level – possessing up to 10,000,000x magnification

- Electron microscopes have contributed most to our understanding of cellular structure and processes – allowing the identification of organelles such as the Golgi apparatus and the nucleolus





8

• It is important to understand how to draw and identify organelles and cell types. Below are labelled examples and some unlabelled version for your practice!





9

Nucleus

Nucleolus

SYNERGY SUCCESS TIP: Make sure to always draw a scale when asked to draw a prokaryotic or eukaryotic cell! It’s one more distinction that can help you get marks, even if your diagram isn’t correct in other places.





10

Passive and Active Transport:

• Before examining the function of the fluid mosaic model of the cell membrane, it is useful to understand passive and active transport and how they differ!

• Passive transport describes the movement of particles from an area where they are in high concentration to an area where they are in low concentration!

- This is often referred to as travelling down a concentration gradient - Passive transport requires no input of energy - There are a few types of passive transport. The two you will focus on are

diffusion and osmosis - Osmosis is the movement of water across a semi-permeable membrane

Note: on the left side of the membrane, there is a high concentration of salt molecules, and therefore a low concentration of water. Water moves from the right to the left so that the concentration of water is equal on both sides.

- Diffusion is the movement of any molecules along a concentration gradient,

such as when a drop of food dye is placed water

• Active transport describes any movement against a concentration gradient (from an area of high concentration to an area of low concentration), and thus requires the input of energy.

- Adenosine Triphosphate (ATP) is the energy unit of all living organisms

• Investigate a variety of prokaryotic and eukaryotic cell structures, including but not limited to: - Modelling the structure and function of the fluid mosaic model of the cell

membrane





11

Fluid Mosaic Model – Function of the Cell Membrane:

• Cells have many basic requirements, and for them to receive these their membrane must have some particular functions.

• The cell membrane serves to protect the cell from undesirable external conditions and controls the movement of substances into and out of the cell (including wastes).

- Substance that the cell requires or needs to remove come in many forms. - Some are dissolved in water, like salt, others are insoluble such as lipids and

most proteins, and some are transported as gases, like oxygen and carbon dioxide.

- These different forms need to be able to pass through the cell membrane easily

• The cell membrane must also be flexible, to allow the cell to contract and expand as the cell’s contents change.

- Cells that become too full often undergo lysis (meaning their membrane ruptures) which leads to cell death.

Fluid Mosaic Model – Structure: The phospholipid bilayer:

• Phospholipids are molecules consisting of a phosphate head and a lipid (fatty acid) tail - A typical phosphate is soluble in water or hydrophilic (water-loving) - A typical lipid is insoluble in water or hydrophobic (water-fearing) - The combination of the two forms a molecule that is amphipathic (both

hydrophobic and hydrophilic)

• This amphipathic quality means that groups of phospholipids undergo ‘self-assembly.’ - The phospholipids arrange into a two-layered sphere so that the hydrophilic

phosphate heads face out towards water and the hydrophobic lipid tails face inwards

- The phospholipid bilayer is used not only for cell membranes but internal membranes of organelles like the liposome as well!





12

Cholesterol:

• Cholesterol is a steroid (a type of hormone) that manages the fluidity of the phospholipids

- Remember that in the phospholipid bilayer, no bonds are formed between the phospholipids making the molecules move laterally (sideways) fluidly

- This could be a disadvantage if the phospholipids become too spaced apart and unwanted substances enter the cell, or if the space becomes too small and substances the cell requires cannot enter!

- Cholesterol helps to manage the changes in membrane fluidity associated with temperature





13

Proteins:

• There are many types of proteins in the cell membrane! All these proteins are controllers of movement into and out of the cell.

• Intrinsic proteins (sometimes called integral proteins) are embedded in the membrane and extend across both layers of the membrane.

- These proteins are most useful for transporting molecules into and out of the cell

- There are many types of intrinsic proteins: - Protein channels facilitate the passive movement of large particles – this is

called facilitated diffusion - Carrier (transport) proteins assists in the active transport of molecules - Receptor proteins receive chemical signals from outside the cell that triggers

a chemical response, achieving intercellular communication

• Extrinsic proteins (sometimes called peripheral proteins) are embedded in the membrane but don’t extend across the entire membrane – these help with communication

SYNERGY SUCCESS TIP: Intracellular and intercellular are often confused! This is a great fact to make flashcards for, after practicing this, it should be second nature! Intracellular = intra (on the inside), cellular (relating to cells) = inside one cell Intercellular = inter (between), cellular (relating to cells) = between cells





14

Glycoproteins and Glycolipids:

• Glycoproteins and glycolipids are formed when a carbohydrate molecule attaches to the surface of a protein or lipid

• Glycoproteins serve as antigens which allow organisms to recognise self and non-self cells, and control some aspects of the immune response

• Glycoproteins and glycolipids also serve as receptor molecules, binding to some hormones which affect the functioning of the cell

Fluid Mosaic Model – General: Transport through the Membrane:

• In general, the structure of the membrane and the fluidity of the phospholipid bilayer allows small, uncharged particles to move by passive transport through the membrane

• Large or charged must cross the membrane through special pathways, such as protein channels.

• Glycoproteins and glycolipids also serve as receptor molecules, binding to some hormones which affect the functioning of the cell





15

Prokaryotic vs Eukaryotic Membranes:

• Recall that eukaryotic cells are much more complex and have advanced structural and functional roles – including intercellular communication (as prokaryotes are unicellular organisms)

• Eukaryotic membranes consist of over 6 types of phospholipids, while prokaryotes only have a few.

• Cholesterol is also not often present in prokaryotic membranes. The making of the model:

• Why do scientists use models? - To represent something too small or too large to be observed - To explain something complex in a simple manner - To make predictions of expected results

• The phospholipid bilayer is so thin it can barely even be seen by an electron microscope, even 100,000x magnification shows merely a double line around 7 nm wide.

• Since we cannot properly see a cell membrane, we create a model using the known properties and essential functions of the membrane.

• The fluid mosaic model was only proposed in 1972, making it a relatively recent discovery – but one that almost perfectly explains cellular functioning and transport!

• The model also allows scientists to predict how particular substance will react with a cell i.e. Will it cross the membrane? Will it cross the membrane through passive or active transport? Will the substance bind with receptors and cause a chemical reaction?

preliminary biology - synergyhsc.com · notes preliminary biology module 1: cells as the basis of...

Documents