23 pages of IB Biology HL Topic 1 (Cell Biology) notes according to syllabus points. Includes key points, explanations, examples, definitions, and diagrams. Easy to understand and organised!
Answer: - fibres are formed from multiple muscle cells fused together
- multiple nuclei surrounded by a single plasma membrane
- fibres are longer than typical cells (300mm)
4.
Why don\'t striated muscle cells follow the cell theory?
Answer: they challenge the concept that cells work independently
5.
Why is giant algae atypical?
Answer: - very large (>70mm)
- complex structure composed of rhizoid, stalk, cap
- consists of one cell with a single nucleus in the rhizoid
6.
Why don\'t giant algae follow the cell theory?
Answer: they challenge the concept that most unicellular organisms are small in size and simple in structure
7.
Why is aseptate fungal hyphae atypical?
Answer: - very large
- no septa, so the cells are multinucleated with continuous cytoplasm along the hyphae
- cell walls made of chitin
- fungal cells have no end wall, making them appear as one cell
8.
Why don\'t aseptate fungal hyphae follow the cell theory?
Answer: they challenge the concept that living structures are composed of discrete cells
9.
What is 1mm in micrometers?
Answer: 1000 micrometers
10.
What is 1000 nanometers in micrometers?
Answer: 1 micrometer
Content preview
1.1 - Introduction to Cells
Cell Theory: a unifying (universally accepted) concept
- All living things are composed of cells
- Cells come from pre-existing cells
- Cells are the basic unit of life
Cells vary in size and shape, but they share certain common characteristics:
- Every living cell is surrounded by a membrane which separates the cell contents from
everything else outside the cell
- Cells contain genetic material which stores all of the instructions needed for the cell’s
activities
- Have chemical reactions catalyzed by enzymes produced inside the cell)
- Cells can produce ATP through respiration to power all the cell’s activities
Atypical examples that don’t follow the cell theory:
1. Striated muscle cells
- Fibres are formed from multiple
muscle cells fused together
- Multiple nuclei surrounded by a
single plasma membrane
- Fibres are longer than typical cells
(300mm)
- Challenges the concept that cells work independently
2. Giant algae (Acetabularia)
- Gigantic (>70mm)
- Complex structure (made up of rhizoid, stalk, and cap)
- Consists of one cell with a single nucleus located in the rhizoid
- Challenges the concept that most unicellular organisms are small in size and
simple in structure
3. Aseptate fungal hyphae
- Very large
- No septa, so the cells are
multi-nucleated with continuous
cytoplasm along the hyphae
- Hyphae are surrounded by cell
walls composed of chitin
- Fungal cells have no end walls,
making them appear as one cell
- Challenges the idea that living
structures are composed of
discrete cells
Magnification
Magnification = size of the image
actual size of specimen
1mm = 1000µm (micrometres) 1µm = 1000nm (nanometres)
,7 functions of life in Paramecium (unicellular organism): MR H GREN
Metabolism Most metabolic pathways happen in the cytoplasm
Response The wave action of the cilia moves the Paramecium in response to stimuli
Homeostasis The contractile vacuole fill up with water and expel through the plasma
membrane to manage the water content
Growth After consuming and assimilating biomass from food, the Paramecium will
get larger until it divides
Reproduction After nuclear division (mitosis) occurs, the two nuclei formed are
separated by constriction of the cytoplasm
Excretion Metabolic waste products expel or diffuse out the cell through the plasma
membrane
Nutrition Food vacuoles contain organisms that the Paramecium has consumed
7 functions of life in Chlorella: MR H GREN
Metabolism Most metabolic pathways happen in the cytoplasm
Response Chlorophyll pigments located in the chloroplast absorb light
Homeostasis Extra glucose is stored as starch in pyrenoids (in chloroplast) to maintain
the osmotic potential of the cell
Growth After consuming and assimilating biomass from food, the Chlorella will get
larger until it divides
Reproduction Mitosis produces autospores that are released when the parent cell wall
breaks down
Excretion Metabolic waste products diffuse out the cell through the plasma
membrane
Nutrition Photosynthesis occurs inside the chloroplasts to provide the algae with
food
, Surface area to volume ratio in cells
Rate of metabolism - volume
Rate of material exchange - surface area
- When a cell increases in size, the SA:Volume ratio decreases because the plasma
membrane will not have enough SA to support the rate of diffusion required for the
increased volume
- Surface area is determined by the plasma membrane
- As the cell grows, volume (rate of metabolism) increases faster than surface area
(rate of material exchange)
- If the metabolic rate is greater than the rate of material exchange, the cell will
eventually die
- Big cell = small SA:Vol ratio
- Hence the cell must divide to maintain a high SA:Vol ratio and survive
- The greater the SA:Vol ratio, the faster the cell can remove waste and heat through
the plasma membrane, and absorb oxygen and nutrients essential for proper
functioning.
Sphere-shaped cells have the largest SA:Vol ratio because when nutrients diffuse into the
cell, they would have to travel the least distance to reach the centre. Nutrients and wastes
are always exchanged at the periphery of the cell.
Benefits and limitations of using cubes to model SA and Vol of cells:
Benefits - Cubes are easily measured while cells have various shapes and sizes that are
difficult to measure
Limitation - Most cells are not cubic in shape
Surface area to volume ratio of prokaryotic cells:
Prokaryotic cells have a large SA:Vol ratio which allows them to meet the cell’s energy
requirements through respiration that occurs across the plasma membrane only.
Surface area to volume ratio of eukaryotic cells:
Eukaryotic cells are far larger than prokaryotic cells, so they have a smaller SA:Vol ratio.
They have mitochondria that have a huge membrane surface area in which enough proteins
for respiration can be embedded to meet the larger cell’s needs.
Adaptations that maximize surface area to volume ratio:
- Thin, flattened shape
- Microvilli
- Long extensions of the cell membrane
Unicellular organisms - organisms consisting of only one cell
Unicellular organisms carry out all functions of life in that cell (MR H GREN), so their
structure is more complex than most cells in multicellular organisms.
Eg. prokaryotes (bacteria)
Multicellular organisms - organisms consisting of many cells
In multicellular organisms, specialised cells of the same type group together to form tissues
through cell differentiation
Eg. most eukaryotes (animal, plant, fungi cells)
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