IB Biology Unit 1

A

Cells:

  • The smallest unit of life

  • Living

  • Bacteria

    • One cell big

  • Protists

    • One cell big

  • Viruses: 

    • not made up of cells

    • need a host to function

    • protein+dna/rna

A2.2 Cell structure

2.2.1: Cells as the basic structural unit of all living organisms

  • Cell theory:

    • All living organisms are made of cells

      • Multi or unicellular

    • Basic unit of life

    • Come from pre-existing cells

  • History of Cell Theory

    • Robert Hooke:

      • Colleague of Antoine

      • Physics, chemistry and biology

      • Named the cell

      • Tense relationship between Hooke and Newton

        • Hooke accused Newton of stealing his work

    • Matthias Schleiden

      • The Cell Theory

      • Botanist

      • Discovered every plant is made of cells

    • Theodor Schwann

      • Schwann cells

      • Studied animal cells

      • Discovered all animals were made of cells

      • The Cell theory

    • Zac Jensen:

      • First microscope

    • Antoine

      • discovered bacteria (animalcules)

    • Virchow 

      • figured out that cells came from cells

    • Louis Pasteur

      • Did an experiment to prove that cells came from cells

A2.2.3 Microscope

Developments in microscopy

  • Staining

    • Improve visibility

    • Uses dye or iodine

  • Immunofluorescence

    • made antibodies that bind to target areas and make them more visible

  • Freeze fracturing

    • Freeze the specimen using liquid nitrogen, causing it to crack, exposing the insides of the specimen. Able to reform it.

  • Cryogenic electron microscopy

    • Able to see the 3D structure of proteins

    • electron gun shoots electrons through the sample

    • high-tech camera catches the image and projects it

    • Specimen can be moving

  • Calculating magnification

    • Scale bar=μm, so convert ruler to μm

    • 1mm = 1000 μm so 20mm = 20,000 μm

    • To calculate magnification

      • scale bar measurement/scale bar label = 20,000 μm/ 10μm

      • magnification = 2,000 times

  • Calculating actual size

    • measure the part of the image you are instructed to and divide it by the magnification

    • convert to the most appropriate units

    • measured length/magnification

    • ex: 80mm/90,000 = 8.9 × 10^-4mm OR 0.00089mm

      • converts to 0.89μm

  • Examples

    • A sperm cell has a tail 50μm long. A student draws it 75mm long. What is the magnification?

      • 1. Convert to μm

        • 75mm = 75,000 μm

      • 2. Drawing length/scale bar label

        • = 75,000/50

        • = 1500x magnification

A2.2.4 Structures common to cells in all living organisms

Prokaryotes

  • Simplest type of cell

  • The oldest type of cell appeared about four billion years ago

  • The largest group of organisms

  • Unicellular organisms that are found in all environments

  • No nucleus

  • Eubacteria and Archaea

  • Simple cell structure without compartments

  • Instead of a nucleus, they have a nucleoid

  • Shapes

    • Cocci = Spherical

    • Bacillus = Rod shaped

    • Spirilla = Spiral

A2.2.5 Prokaryotic cell structure

  • 1. Draw and Label (know at least 5)

Labeling

  • 2. annotate (explain their functions)

Peptidoglycan: The protein that makes up the cell wall of a prokaryotic cell

Pili: useful for conjugation (exchange of genetic material)

Plasmids: what is being exchanged through pilids

A2.2.6 Eukaryotic cells

  • Organisms whose cells have a nucleus

  • All animals, plants, fungi and many unicellular organisms are eukaryotes

plant cell

Cell Membrane

  • boundary of cell

  • gatekeeper

    • prevents entry or exit of molecules

    • phospholipid bilayer

    • permeable to oxygen and co2

    • impermeable to water and charged particle, must enter through special proteins embedded in the membrane

Nucleus

  • has chromosomes which make up most of the DNA in a cell

  • largest organelle

  • double layer membrane

  • mRNA, transcribed from DNA in nucleus exits through pores

  • can be multiple nuclei

Golgi apparatus

  • packaging and delivery of proteins

Lysosomes

  • simple, membrane bound organelles full of enzymes that digest engulfed bacteria and viruses and large molecules for recycling

  • Breaks down things that shouldn’t be in the cell

Mitochondrion:

  • Powerhouse of the cell

  • Has a smooth outer membrane and a folded inner membrane

  • Where aerobic respiration occurs

  • Converts sugars into ATP

Free ribosomes

  • 80s sized in eukaryotes (70s size in prokaryotes)

    • Ribosomes in bacteria have different ribosomes

    • ‘s’ is a unit

    • means bigger

  • Proteins synthesized for use within the cell (enzymes used in the cytoplasm)

Chloroplasts

  • Site of photosynthesis in plant cells

  • Stacks of thylakoids

  • exist in algae as well

Vacuoles and vesicles

  • Animal cells sometimes have small vacuoles (vesicles) for digestion

  • Unicellular organisms have contractile vacuoles for expelling water

  • plant cells have large vacuoles that hold water and food

  • vesicles are small lipid sacs used for transport

  • vacuoles are large

Centrioles

  • Bundles of microtubules found in animal cells

  • Pull stuff in the nucleus to the side

  • Help cells divide

Microtubules

  • Separate chromosomes in cell division and make up cilia and flagella

  • What centrioles are made out of

Flagella:

  • occur in bacteria

  • make bacteria move

  • occur in eukaryotic cells some times

Cillia:

  • Used for movement

  • only in eukaryotic

A2.2.7 Processes of life in unicellular organisms

  • Functions of Life

  • Metabolism

  • Reproduction

  • Homeostasis

  • Response

  • Excretion

  • Nutrition

  • Growth

Paramecium

  • Heterotroph

  • surrounded by cilia

  • take in food through specialized membranous feeding groove called a cytostome

  • food particles are enclosed in vesicles

  • solid wastes are removed through an anal pore while liquid through urine

  • essential gasses enter and exit the cell via diffusion

  • paramecia divide asexually (fission) although horizontal gene transfer can happen via conjugation (pili)

A2.2.8 Differences in eukaryotic cell structure between animals, fungi, and plants

  • Eukaryotes have been classified into kingdoms, based on key structural and functional differences

    • Animal:

      • no cell wall and undertake heterotrophic (ingestion) nutrition

    • Plant:

      • have a cell wall (cellulose) and undertake autotrophic nutrition (photosynthesis)

    • Fungi:

      • Have a cell wall made of chitin and undertake heterophic nutrition (absorption)

  • Protist:

    • Any eukaryotic organism that does not belong to the animal, plan, or fungal kingdoms (hetero and autotrophic)

A2.2.9 Atypical cell structure in eukaryotes

  • Red blood cells don’t have a nucleus

  • Striated muscle

    • Multinucleate

    • Composed of long muscle fibres that can measure 300mm or more and are larger than regular cells

    • Atypical, as each muscle fibre contains hundreds of nuclei, and each cell does not function independently

  • Aseptate fungi

    • Normal fungi have thread-like structures

    • does not have individual/discrete cells

  • Phloem

    • Sieve tube element

    • Comparison cell

    • Because sieve tubes do not contain a nucleus

  • Sieve tube elements

    • Found in plants and transports liquid nutrients in phloem

    • Lack a nucleus and have very few ribosomes

B Organelles and compartmentalization

B2.2.1 Eukaryotic organelles as discrete subunits of cells that are adapted to perform specific functions.

  • NOS Progress in science often follows the development of new techniques

    • Differential centrifugation

      • Separation technique that includes spinning things very quickly

      • Used for cell fractionation

        • separates organelles

      • works because different stuff has different densities

B2.2.2

  • Eukaryotes have their DNA safe inside the nucleus.

  • Allows for multiple linear chromosomes, which efficiently pack the whole DNA.

  • In eukaryotes DNA needs to be transcribed into RNA before it can leave the nucleus.

  • Allows for modification of the RNA before translation.    

  • Does not occur in prokaryotes

B2.2.3

  • Advantages of compartmentalization in cytoplasm cells

    • Enzymes and metabolites can be concentrated in a small space, increasing the chance for collision between active site and substrate

    • Substances that can damage cells can be isolated within a membrane, protecting remaining structures from degradation

    • Conditions, such as pH, can be maintained at an optimal value for a particular reaction

    • Large areas of membrane can become dense with proteins for a specific process

B2.3.1

  • Following fertilisation, an unspecialised zygote will divide and develop into a mass of specialised cells (early embryo) via differentiation

  • This process is driven by the release of gene-regulating chemicals

(transcription factors) called morphogens

  • In humans, 220 distinct highly specialised cell types have been recognised

  • All specialised cells and the organs constructed from them have developed as a result of differentiation

B2.3.2

  • Properties of stem cells

    • Undifferentiated

      • cells with the ability to divide endlessly and differentiate along different pathways

    • A single cell that can replicate itself or differentiate into many cell types

    • No job

    • All cells in an organism share the same genome

    • Some cells differentiate, that is grow and mature into different specialized cells

    • By only activating some of the genes in the genome during differentiation, cells can become specialized cells

    • Video notes

      • What?

        • cells that are undifferentiated, no job or function

      • Why are they useful?

        • potential to become all other kinds of cells

        • replaces dead cells

        • regenerative medicine

      • How many types?

        • tissue specific (adult)

          • replace existing cells in organs

          • totipotent

          • differentiate into limited types of cells

        • embryonic    

          • pluripotent

            • can differentiate into any type of cell

        • induced pluripotent

          • can become any cell in the body

          • artificially created from adult stem cells and can differentiate into many other cells

      • Why is their use controversial?

        • certain religious groups are against using potential life for research and medical research

  • All cells in an organism share the same genome (entire set of genetic

instructions)

  • Some cells differentiate , that is grow and mature into different specialized

cells

  • By only activating some of the genes in the genome during differentiation,

cells can become specialized cells

B2.3.3

B2.3.3

  • Location and function of stem cell niches in adult humans

    • sites in the body where a pool of adult stem cells are maintained in preparation for future proliferation and differentiation

    • in bone marrow, hair follicles, heart, intestines, and brain

    • bone marrow

      • give rise to different types of blood cells (erythrocytes - red blood cell, and leukocytes - white blood cell)

      • commonly used to treat leukemia

    • Hair follicles

      • have a range of epidermal stem cells that are used for hair growth, skin innervation, vascularization and wound repair

      • treat severe burns and hair regrowth

B2.3.4

  • Totipotent

    • can differentiate into any type of cell

      • zygote

  • Pluripotent

    • can differentiate into many types of cells but not all

  • Multipotent

    • can differentiate into a few closely related types of cells

      • bone marrow

  • Unipotent

    • can regenerate but can only differentiate into their associated cell type

      • Liver stem cells can only make liver stem cells

B2.3.5

Cell size as an aspect of specialization

  • Red blood cells need to squeeze through narrow capillaries and are small

  • neurons need to transmit signals throughout the body and can be very long

  • striated muscle fibres consist of fused muscle cells

  • A human ovum (egg) is one of the largest cells, while sperm is very small

B2.3.6 surface area to volume ratios and constraints on cell size

surface-to-area-to-volume ratios and constraints on cell size

  • The larger the organism, the more exchange has to take place to meet its needs.

  • substances move in/out of a cell through the plasma membrane

  • Big SA:V = big movement across membrane

  • Small SA: Vol = little movement across membrane

  • When volume increases, so does surface area, but not to the same extent

  • As a cell gets larger, the SA: vol ratio gets smaller

    • if the ratio gets too small, the particles won’t be able to enter and exit the cell fast enough