A2.2 Cell structure

a plasma membrane, cytoplasm, DNA, and ribosomes

Subcellular components and viruses

• The cell is the basic unit of life. • All living things are composed of cells. • Cells come from preexisting cells through division.

Unicellular- different parts of the cell are responsible for all life functions (stem cells) Multicellular - different cells arranged together to carry out life functions (tissues, organs)

Paramecium: Heterotroph, engulfs food with oral groove and uses cilia to sweep them in. Digestion occurs in food vacuoles, with enzymes in the cytoplasm. Cilia to move. excreted through diffusion or an anal pore Chlamydomona: Autotroph, large chloroplast containing chlorophyll to perform photosynthesis, producing its own glucose. Flagella to move. Waste excreted through diffusion Both organisms use contractile vacuoles to pump out excess water, maintaining a stable internal environment, both reproduce sexually,

*P no mitochondria or nucleus *P 70S ribosomes *P no compartmentalization in nucleoid region *P <1um *P rigid cell walls *P DNA free in cytoplasm, no protein Similarities: *both cells have plasma membrane *both cells carry out the functions of life *DNA is present in both cells

MRS HENG Metabolism - enzyme-catalyzed reactions Reproduction - production of offspring Sensitivity - react to stimuli in the environment with various responses Homeostasis - maintaining a stable internal environment Excretion - removal of waste products Nutrition - getting nutrients required for growth/maintenance Growth - increasing in size or number of cells

Prokaryotic cells divide by copying DNA then the cell divides into two genetically identical daughter cells. Divisional process includes elongation of the cell

DNA is free in cytoplasm. 1 mark This allows rapid replication/binary fission. 1 mark Rigid cell wall provides protection from osmotic lysis. 1 mark Rigid cell wall provides structural support. 1 mark Rigid cell wall provides shape maintenance. 1 mark Presence of flagella enables movement towards nutrients/favorable conditions. 1 mark Presence of flagella enables movement away from harmful substances. 1 mark Plasmids contain additional genes for antibiotic resistance. 1 mark

*Nucleoid region is non compartmentalized, as a simpler structure makes a membrane unnecessary and inefficient *contains a single, long, continuous, circular thread of DNA *may also contain plasmids (smaller circular DNA molecules)

prokaryotic DNA. genetic material that is not associated with histone proteins for packaging, meaning it is free within the cytoplasm in a region called the nucleoid.

Cell wall: Plants – cellulose; Fungi – chitin; Animals – none Vacuoles: Plants – large central; Fungi – small; Animals – small or none Chloroplasts: Plants – present for photosynthesis; Fungi & Animals – absent Centrioles: Animals – present; Plants – usually absent; Fungi – usually absent Undulipodia (Cilia & Flagella): Animals – sometimes present (movement); Plants – rare (some sperm); Fungi – rare, mainly in reproductive spores

The cytosol is mostly water Cytoplasm is a collective term for the cytosol plus the organelles suspended within the cytosol.

Viruses: Lacks organelles necessary for independent life Striated muscle fibers: Contain multiple nuclei within a single, continuous cell for a greater DNA template for producing the large amounts of proteins, Aseptate fungal hyphae: continuous, multinucleated tube of cytoplasm allows for the rapid and efficient movement of nutrients, growth Phloem sieve tube: Minimal cellular components (nuclei, ribosomes, cytoskeleton, and cytoplasm) as kept alive with companion cells (full living cells) Red blood cells: Lack a nucleus and other organelles to maximize the space for carrying hemoglobin

1m= 1000 mm 1mm=1000μm 1μm=1000 nm

Eyepiece – The point through which the magnified image is observed (contains ocular lens) Focus Mechanism – Responsible for resolving the image (may include both fine and coarse focus adjustments) Revolving Nosepiece – Rotating device that allows for selection of objective lens Objective Lens – Magnifies image of specimen (in conjunction with ocular lens) Stage – Platform on which specimen is positioned (specimen is usually affixed to a glass slide) Stage Clips – Holds specimen in place (some mechanical stages can be moved to reposition slide while viewing) Iris Diaphragm – Regulates the intensity of light that is projected onto the slide Light Source – Either external (redirected by mirrors) or internal (light bulb within the microscope base)

L takes minutes to hours, E takes days L can be alive, E has to be dead L coloured by dyes, E covered with electrons L has magnification 500x-1000x, E up to 100000x L does not require vacuum, E require vacuum L seen by eyes, E seen by fluorescent screen

i = m * a

Brightfield: specimen viewed against a light background Darkfield: specimen appears light in dark background Phase-contrast: circular diaphragm and modified objective lens to show detailed specimen without staining

*Electron microscopes use electrons instead of light for higher resolution *Cryogenic freezes cells (ex. viruses) in 3D form to look at the structure *Freeze Fracture rapid freezes and then breaks apart to see what would happen if a membrane was frozen

Fluorescent stains absorb then re-emit light at a different wavelength allowing researchers to see them clearly against a dark background.

Prokaryotic Light: Can be arranged in groups or chains, Small <5μm, helical, spherical, or rod shaped Electron: Close up examination of organelles Animal Light: Variable in shape but typically rounded Electron: Close up examination of organelles Plant Light: Multicellular, Larger >5μm Large water vacuole Electron: Close up examination of organelles

Lysosomes contain hydrolytic enzymes. These enzymes break down macromolecules, damaged organelles, and pathogens The process is called intracellular digestion, of autophagy Breakdown products are recycled as building blocks for new molecule Lysosomes remove waste materials to maintain cellular health Recycling conserves resources and energy, contributing to homeostasis