UNIT 1.1 Flashcards
What 3 things does the cell theory state?
All living things are composed of cells (or cell products)
The cell is the smallest unit of life
Cells can only arise from pre-existing cells
Name 3 common caveats to the cell theory
Striated Muscle Fibres
Aseptate Fungal Hyphae
Giant Algae
How is striated muscle fibre a caveat to the cell theory?
Muscle cells fuse to form very long fibres (>300mm).
Consequently, they have multiple nuclei despite being surrounded by a single, continuous plasma membrane.
This challenges the idea that cells always function as autonomous units.
How is Aseptate Fungal Hyphae a caveat to the cell theory?
Fungi may have filamentous structures called hyphae, separated into cells by internal walls called septa.
Some fungi are not partitioned by septa & hence have a continuous cytoplasm along the length of the hyphae.
This challenges the idea that living structures are composed of discrete cells.
How is Giant Algae a caveat to the cell theory?
Certain species of unicellular algae may grow to very large sizes (Acetabularia - 70mm)
Challenges the idea that larger organisms always consist of many microscopic cells.
What are the functions of life ?
Metabolism – Living things undertake essential chemical reactions
Reproduction – Living things produce offspring, either sexually or asexually
Sensitivity(Response) – Living things are responsive to internal and external stimuli
Homeostasis – Living things maintain a stable internal environment
Excretion – Living things exhibit the removal of waste products
Nutrition – Living things exchange materials and gases with the environment
Growth – Living things can move and change shape or size
MR SHENG
How does the unicellular organism Paramecium (Heterotroph) carry out the functions of life ?
- Surrounded by small hairs called cillia which allow it to move (Responsiveness / Growth).
- Engulf nutrients via specialised feeding groove called a cytostome (Nutrition).
- Nutrient particles are enclosed within small vacuoles containing enzymes for digestion (Metabolism).
- Solid Wastes are pumped out via contractile vacuoles (Excretion).
- Essential gases enter (e.g. O2) & exit (CO2) the cell via diffusion (Homeostasis).
- Paramecia divide asexually (fission) although horizontal gene transfer can occur via conjugation (reproduction).
How does the unicellular organism Scenedesmus (Autotroph) carry out the functions of life ?
- Scenedesmus exchange gases & other essential materials via diffusion (Nutrition/Excretion/Homeostasis)
- Chlorophyll pigments allow organic molecules to be produced via photosynthesis (Metabolism).
- Daughter cells form as non-motile autospores via the internal asexual division of the parent cell (Reproduction)
- Scenedesmus may exist as unicells or form colonies for protection (Responsiveness).
Explain how SA:VOL ratio limits cell size
- Metabolism requires exchange of materials with the environment.
- The rate of metabolism of a cell is a function of it’s mass/volume (larger cells need more energy).
- The rate of material exchange is a function of it’s surface area (larger membrane surface = more material movement).
- As a cell grows, volume increases faster than cell surface area, leading to decrease in SA:VOL ratio.
- If the rate of metabolism exceeds the rate of exchange of vital materials/waste, the cell will eventually die.
- Hence growing cells tend to divide in order to remain small (In order to maintain higher SA:VOL ratio.
Provide 3 examples of how SA:VOL ratio is increased within organisms.
- Cells & tissues that are specialised for gas or material exchange will increase their surface area to optimise material transfer.
- Intestinal tissue of the digestive tract may form a ruffled structure (villi) to increase the SA of the inner lining.
- Alveoli within the lungs have membranous extensions called micro villi, which function to increase the total membrane surface.
What is the formula used to calculate magnification?
Magnification = Image size (With Ruler) / Actual size (according to scale bar)
What is the formula used to calculate actual size ?
Actual Size = Image size (With Ruler ) / Magnification
Compare the use (Pros and Cons) O=of using light/electron microscopes
Light;
-Living specimens can be observed in their natural colour
-Dyes and fluorescent markers can be used to resolve specific structures.
-Far cheaper and far more accessible.
Electron Microscopes;
-Have much higher resolution and magnification than light microscopes.
-Transmission electron microscopes (TEM) can be used to create a cross section.
-Scanning Electron Microscopes (SEM) can be used to differentiate depth and form a 3D image.
What is meant by ‘Emergent Properties’?
Multicellullar organisms are capable of completing functions that unicellular organisms could not undertake – this is due to the collective actions of individual cells combining to create new synergistic effects
Explain (The process of) Cell differentiation
Differentiation is the process in development whereby newly formed cells become more specialised, and distinct from other cells; expressing characteristics that aid the cells purpose.
Since all cells contain an identical genome, differentiation occurs as the result of specific genes being activated by chemical signals.
