Biology - Cell Theory, Prokaryotes and Viruses

What is the Cell Theory? (3)

All living organisms are composed of cells and they may be unicellular or multicellular, cells are the basic unit of life, cells arise from pre-existing cells

What are Prokaryotes? (3)

single-celled organisms, usually lacking membrane-bound organelles, with DNA free in the cytoplasm

What do Prokaryotes include? (2)

bacteria and archaea

features of a typical prokaryotic bacterial cell (9)

cytoplasm, mesosome, circular DNA, plasmid, 70S ribosomes, flagella, pili, slime coat, peptidoglycan wall

mesosome (3)

where respiration occurs, producing ATP, increases the membrane’s surface area so more ATP is produced

plasmid (not always present)

contains additional DNA for things like antibiotic resistance

cytoplasm

where many reactions occur

circular DNA

no nucleus

70S ribosomes

where protein synthesis occurs

flagella

made of flagellin

pili (3)

small hair-like structures, allow bacteria to adhere to each other or to host cells, allow for communication between bacteria

slime coat (2)

helps protect against environmental threat, allows to stick to things like food

peptidoglycan wall

cell wall made of a different carbohydrate to cellulose

What does the Endosymbiotic Theory demonstrate?

How prokaryotes produced eukaryotes

Describe the first stage of the Endosymbiotic Theory (4)

prokaryote ingested aerobic bacteria, they had a symbiotic relationship, because the aerobes were protected from the external environment, and the the aerobes produced energy for the prokaryote

Describe the second stage of the Endosymbiotic Theory

Over a long time aerobes became mitochondria and could no longer survive on their own

Describe how animal cells were produced from the Endosymbiotic Theory

cells contained mitochondria

Describe how plant cells were produced through the third stage of the Endosymbiotic Theory (5)

Some of the prokaryotes engulfed cyanobacteria, that contain photosynthetic pigments, these later on became chloroplasts, the chloroplasts couldn’t live on their own anymore, so plant cells were produced

Mitochondria and chloroplasts contain small loops of DNA similar to plasmids found in prokaryotic cells. These organelles also contain ribosomes that are the same size as prokaryotic ribosomes, can you suggest an explanation for these features? (3)

mitochondria and chloroplasts are derived from prokaryotes, so they contain 70S ribosomes like prokaryotes, so they are also very old

Why are viruses considered non-living? (2)

viruses cannot exist outside a cell, they don’t show characteristics of life

What are characteristics of life that prove viruses are non-living? (7)

movement, respiration, sensitivity, nutrition, excretion, reproduction, growth

What do all viruses consist of? (2)

either DNA or RNA enclosed in a protein coat

What do some viruses also have?

an envelope