A2.2 Flashcards
A2.2.1—Cells as the basic structural unit of all living organisms
The cell theory states that:
* Cells are the smallest unit of life
* All organisms are made of cells
* All cells come from pre-existing cells
A2.2.2—Microscopy skills
TOTAL MAGNIFICATION = OCULAR X OBJECTIVE
M=IA
A2.2.3—Developments in microscopy
Electron Microscope
Light Microscope
Large and installation means it cannot be moved
Small and easy to carry
Vacuum needed
No vacuum needed
Complicated sample preparation
Simple sample preparation
Over x500000 magnification
Up to x2000 magnification
Resolution 0.5nm
Resolution 200nm
Specimens need to be dead
Specimens can be living or dead
Microscope type Advantage(s) Disadvantage(s)
Light microscope Easy to use, inexpensive, allows observation of living organisms Limited resolution (~200 nm), cannot observe smaller structures like organelles
Light microscope using fluorescence Allows visualization of specific structures with high contrast by using fluorescent markers Fluorescence can fade (photobleaching), requires specific staining techniques
Light microscope using immunofluorescence Highly specific targeting of proteins or molecules, enables studying protein localization Complex sample preparation, potential for cross-reactivity of antibodies
Electron microscope Extremely high resolution (up to 0.1 nm), can view ultrastructure of cells and small particles Expensive, requires vacuum and complex preparation, only dead specimens can be observed
Electron microscope using freeze fracture Reveals internal membrane structures and surfaces, preserves cell architecture Technically challenging, can introduce artifacts due to the fracturing process
Cryogenic electron microscope Provides near-atomic resolution, preserves samples in their native hydrated state Extremely expensive, requires complex instrumentation and specialized facilities
A2.2.4—Structures common to cells in all living organisms
Plasma Membrane – All cells must have an outer border to maintain an internal chemistry that is different to the exterior (homeostasis)
Genetic Material – All cells must contain coded instructions (DNA) that function to control internal activities within a cell (metabolism)
Ribosomes – All cells must contain ribosomes in order to translate the cell’s coded instructions into functional elements (proteins)
Cytosol – All cells must contain an internal fluid that functions as a reaction medium for all necessary metabolic processes
A2.2.5—Prokaryote cell structure
- Plasma membrane – phospholipid bilayer surrounding the cell. It controls the movement of materials into and out of the cell.
- DNA – this is the genetic material and is found within a region of the cytosol called the nucleoid. Prokaryotic DNA is found as one large circular chromosome. Prokaryotic DNA is ‘naked’ which means it is not associated with histone proteins.
Prokaryotic cells may also have additional DNA molecules known as plasmids. Plasmids are small, circular pieces of DNA that contain only a few genes often associated with antibiotic resistance. - Ribosomes – made up of protein and rRNA, ribosomes are the site of protein synthesis within the cell. In prokaryotic cells, ribosomes are small in size (70S).
- Cell wall – made of peptidoglycan and found surrounding the plasma membrane. The cell wall provides structure and support for the cell.
Some prokaryotic cells also contain an additional outer layer known as the slime capsule. - Pili – these hair-like extensions are found in some prokaryotic cells and are involved in either adhesion to surfaces or plasmid exchange.
- Flagella – long whip-like ‘tails’ are found in some prokaryotic cells and are used to facilitate movement.
A2.2.6—Eukaryote cell structure
- Plasma membrane – phospholipid bilayer surrounding the cell. It controls the movement of materials into and out of the cell.
- Nucleus – made of a double membrane with pores. The nucleus contains the DNA which is found in the form of linear chromosomes. Eukaryotic DNA is associated with histone proteins.
- Ribosomes – site of protein synthesis. Can be found free within the cytoplasm or attached to the rough endoplasmic reticulum. In eukaryotic cells, ribosomes are large in size (80S).
- Mitochondria – site of aerobic cellular respiration.
- Endoplasmic reticulum – interconnected membranes either involved in protein synthesis (rough ER) or lipid synthesis (smooth ER).
- Golgi apparatus – flattened membrane sacs involved in the modification and packaging of proteins.
- Vesicles or vacuoles – membrane-bound sacs involved in storage and transport. Generally vacuoles are larger than vesicles, and while vesicles are able to fuse with other membranes in the cell, vacuoles do not.
- Cytoskeleton – made of microtubules and microfilaments. Provides a structural framework for cells giving the cell its overall shape, positions organelles, transports vesicles around the cell, and allows movement in some cells.
Additionally, some eukaryotic cells also have the following: - Cell wall – made of cellulose (plant cells) or chitin (fungal cells) and found surrounding the plasma membrane. The cell wall provides structure and support for the cell.
- Flagella – long whip-like ‘tails’ found in some unicellular eukaryotic cells and allow for movement.
- Lysosomes – vesicles containing digestive enzymes that fuse with other vesicles to allow for the digestion of damaged organelles or engulfed materials. These vesicles are found in animal cells.
- Chloroplasts – site of photosynthesis in plant cells.
A2.2.7—Processes of life in unicellular organisms
Metabolism –essential chemical reactions such as cellular respiration.
· Reproduction –produce offspring either sexually or asexually.
· Sensitivity – respond to internal and external stimuli.
· Homeostasis –maintain a stable internal environment.
· Excretion – remove waste products.
· Nutrition – obtain required materials from their environment.
· Growth – increase in size.
· Movement – move and change shape or size.
Mrs. M Heng
Metabolism Reproduction Sensitivity Movement Homeostasis Excretion Nutrition Growth
A2.2.8—Differences in eukaryotic cell structure between animals, fungi and plants
Animal cells Fungal cells Plant cells
Nutrition Heterotrophic (consume organic materials) Heterotrophic (decomposers, absorb organic materials) Autotrophic (photosynthesis using chloroplasts)
Presence and composition of cell walls No cell wall Yes, composed of chitin Yes, composed of cellulose
Differences in size and function of vacuoles Small, mainly involved in storage and waste removal Large central vacuole, involved in storage and maintaining turgor pressure Large central vacuole, helps maintain turgor pressure and stores nutrients
Presence of chloroplasts, plastids, and lysosomes Lysosomes present, no chloroplasts or plastids Lysosomes present, no chloroplasts or plastids Chloroplasts and plastids present, lysosomes absent
Presence of centrioles Present Absent Absent
Presence of cilia and flagella Present in some cells (e.g., sperm cells) Absent in most, but some may have flagella Absent in most plants, present in some algae
A2.2.9—Atypical cell structure in eukaryotes
atypical cells - multnucleate
skeletal muscle and fungal hyphae
atypical cells - no nucleus
phloem sieve tube
red blood cells
A2.2.10—Cell types and cell structures viewed in light and electron micrographs
Students should be able to identify cells in light and electron micrographs as prokaryote, plant or animal. In electron micrographs, students should be able to identify these structures: nucleoid region, prokaryotic cell wall, nucleus, mitochondrion, chloroplast, sap vacuole, Golgi apparatus, rough and smooth endoplasmic reticulum, chromosomes, ribosomes, cell wall, plasma membrane and microvilli.
https://old-ib.bioninja.com.au/standard-level/topic-1-cell-biology/12-ultrastructure-of-cells/cell-micrographs.html
A2.2.11—Drawing and annotation based on electron micrographs
- Draw, annotate and describe observed cells and organelles.
- Estimate the size of cells and organelles.
- Calculate the magnification of a diagram
A2.2.12—Origin of eukaryotic cells by endosymbiosis
Evidence suggests that all eukaryotic cells evolved from a common unicellular ancestor that had a nucleus and reproduced sexually. The nucleus would have been formed through infolding of the plasma membrane. Mitochondria then evolved by endosymbiosis. In some eukaryotes, chloroplasts also evolved by endosymbiosis after the mitochondria.
Evidence suggests that all eukaryotes evolved from a common unicellular ancestor that had a nucleus and reproduced sexually. Mitochondria then evolved by endosymbiosis. In some eukaryotes, chloroplasts subsequently also had an endosymbiotic origin.
Describe two pieces of evidence that show that eukaryotic cells originated by endosymbiosis.
mitochondria/chloroplasts have their own DNA;
mitochondria can self-replicate/undergo a process like binary fission;
mitochondria/chloroplasts have double membranes;
mitochondria/chloroplasts have(70s) ribosomes;
mitochondria/chloroplasts are sensitive to antibiotics;
similar in size to bacteria
Evidence for the theory of endosymbiosis can be found in both the mitochondria and chloroplasts of eukaryotic cells. This evidence includes:
* Presence of a double membrane
* Presence of 70S ribosomes.
* Naked, circular DNA present.
* Ability to replicate in a process similar to binary fission.
A2.2.13—Cell differentiation as the process for developing specialized tissues in multicellular organisms
Multicellular organisms exhibit emergent properties; the sum of the whole is greater than the individual parts. This means that a multicellular organism is capable of completing functions that unicellular organisms are not. They can do this through having the same specialised cells grouped together to form tissues, different tissues forming organs, and organs interacting to form organ systems.
The cells of multicellular organisms are able to specialise and develop unique functions. They do this through the differential expression of genes.
A2.2.14—Evolution of multicellularity
All plant and animal species, and most fungal species are multicellular. Multicellularity has evolved a number of times.
Being multicellular provides a number of advantages:
* Multicellular organisms can become much larger than unicellular organisms as the limitations of SA:Vol ratios do not apply.
* Multicellular organisms have longer lifespans as they can survive the death of individual cells.
* Multicellular organisms are more complex due to differentiation into different cell types within a single organism.
But there is one disadvantage to multicellularity. If the growth of an organism through cell division is not regulated, cancer (uncontrolled cell division) can develop.
