Inquiry Question: What Distinguishes one cell from another?
Cell Theory
All living things are made of cells
Cells are the basic structural and functional units of organisms
All cells come from pre-existing cells
Cell Structure
Classification of cells
Prokaryotes (Unicellular Organisms)
Primitive cells
smaller and simpler than eukaryotic cells
abundance compared to eukaryotic cells
No membrane bound organelles
Divided into two groups → Archaea and Bacteria
Small and efficient→ High SA:V ratio
Four Main Structures:
Cell
Cytoplasm
Ribosomes
Genetic Material → Found in a large loop called the
nucleoid.
Eukaryotes (Unicellular and Multicellular)
More complex and large than prokaryotes
10-100um
Multicellular plants and animals are composed of a variety of
different types of eukaryotic cells
Divided into kingdoms → Amoeba, fungi, Plantae and animalia
Contain membrane bound organelles
Each organelle has a specific function within the cell
Together the organelles carry out all the biochemical
processes and reactions like transpiration and
photosynthesis.
Endosymbiosis
Large prokaryotic cells engulfed smaller prokaryotic cells →
Photosynthesising made chloroplasts + cells that used oxygen to
produce their own energy made a mitochondria
Size of mitochondria and chloroplasts tend to be the same size as
bacteria
The way mitochondria and chloroplasts divide tend to be the same
process as prokaryotes
Organelles
Name
Function
Mitochondria
The mitochondria is the powerhouse of the cell. They produce the energy for the cell known as ATP through cellular respiration. Responsible for creating more than 90% of the energy needed to sustain life. Animals have more than plants. Plants only use their mitochondria at night.
Cytoplasm
Cytoplasm consists of a liquid based background, in which there are dissolved chemical substances (e.g. ions such as chloride ions). Approximately 90 per cent of the cytoplasm is water.
Nucleus
The nucleus is a large spherical oval structure in the cytoplasm. The nucleus is transparent and colourless. There are two main functions for a nucleus including; storing the cell’s DNA and being responsible for the cells growth, reproduction etc. The nucleus produces ribosomes.
Chloroplasts
Chloroplasts are only found in plant cells. Photosynthesis occurs in this section of the cell. The chloroplast uses the sunlight to convert the energy into sugars to power the plant cells. Inside of the chloroplasts there are little green chlorophylls (molecules).
Endoplasmic Reticulum
The endoplasmic reticulum also known as ER is an organelle found in the cells of eukaryotic organisms. ER occurs in nearly every type of eukaryotic cell except red blood cells and sperm cells. There are two types of endoplasmic reticulum rough endoplasmic reticulum (RER) (have ribosomes attached) and smooth endoplasmic reticulum (SER). It is a form of transportation for materials
Vacuoles
Is a sac-like structure that stores materials such as water, ions, wastes and proteins. The size of the vacuoles depends on the shape and size of the cell. They are found in both plant and animal cells, but are larger in plants. Has a membrane
Ribosomes
Ribosomes are a cell structure that assists with making protein. Ribosomes are found floating around in the cytoplasm and/or attached to the rough endoplasmic reticulum.
Golgi Bodies
The golgi body is an organelle found in most eukaryotic cells. There are numerous functions of the golgi such as sorting and processing proteins. They are also responsible for determining which proteins are allowed outside of the cell.
Lysosomes
The main function of lysosomes is to digest and remove waste from the cell. They contain digestive enzymes. They are the stomach of the cell. Lysosomes are surrounded by a layer of lipids acting as a membrane.
Cytoskeleton
Cytoskeleton are present in all cells. They are a complex network of interlinking filaments and tubules throughout the cytoplasm. They supports, shape and helps facilitate movement.
Cell Wall
The cell wall provides support and protection for the cell. They are only found in plant cells. Cell walls lie on the outside of the cell membrane
Technology
Light Microscope
A light source passes through a condenser lens then through the
specimen
The beam of light passes through the convex objective lens, the
image is magnified and viewed through the ocular lens.
Magnification of up to 1500x and maximum resolution of 200nm
Fluorescence Microscope
Better resolution than light microscope
Sample is labelled with a fluorescent dye that attaches to
particular structures
Sample is illuminated with a high intensity source of light that
causes the fluorescent substance to emit light.
Electron Microscope
Uses an electronic beam instead of light and electromagnetism
instead of glass lenses
Greater resolution due to shorter wavelengths
Many cells were seen for the first time with this invention
Computer Enhanced Technology
Microscopic images can be digitally processed to allow cells to be
viewed in different ways
Cells scan software can provide #D images of cell structures.
Biological Drawings
Cell Size (1mm = 1000micrometres)
Size of Object/cells = Field of view / Fit Number
E.g. FOV is 30mm, 3 cells fill it up → Each cell is 10cm wide
Fluid Mosaic Model
Controls the exchange of material between internal and external
environments of the cell
Selectively permeable → Allows certain molecules and ions into and
out of the cell
The structure of it allows the concentration to be constant inside
and outside of the cell
The membrane is not stationary and continuously moving.
Phospholipid Bilayer (Phosphate-Lipid)
Phosphate heads are hydrophilic (able to absorb water)
Lipid tails are hydrophobic (water avoidant and not able to dissolve
in water)
Factors affecting the membrane
Cholesterol
Gives stability to the cell membrane without affecting the fluidity.
Reduces the permeability of the cell membrane to small, water
soluble molecules.
Temperature
As temperature increases, fluidity increases.
Phospholipids become less tightly packed and move more freely
As temperature decreases, cell membranes with a high percentage of
saturated fatty acid may solidify
Proteins
Some penetrate the whole way through the membrane, forming channels
that allow some materials to pass through the membrane.
Receptor proteins cause the cells to respond only to signals from
substances.
Carrier proteins can assist in facilitated diffusion or active
transport (May require energy to go against the concentration
gradient)
Cell Function
Inquiry Question: How do cells coordinate activities within their
internal and external environments?
Movement across cell membrane
○ Chemical properties of the material being moved
○ Physical properties like shape and size
○ Permeability of the cell membrane to the material
○ Concentration gradient → Higher the gradient, faster the movement
○ Surface Area to volume ratio
Diffusion
○ Particles move from a high concentration to a low concentration
○ Movement is slow as particles collide
○ Passive movement → Does not require Energy
○ Factors Influencing diffusion → Particle size, Concentration,
Temperature
○ Simple Diffusion
■ Solute membranes diffuse across a membrane if the membrane is
permeable to them
■ Movement is constant
■ If the concentration is equal on both sides, there is no net movement
○ Facilitated Diffusion
■ Membrane transport proteins are specific for particular particles,
so transport is selective.
■ Transport is more rapid than simple diffusion.
■ Transport proteins can become saturated as the concentration of the
transported substance increases.
■ No energy is required, movement is with a concentration gradient.
■ Require a channel or carrier protein to assist in transport
Osmosis
○ The net movement of water molecules across a semipermeable membrane.
○ If a dilute and concentrated solution are separated by a
semipermeable membrane which allows the movement of free water
molecules, the water molecules will move from the dilute solution to
the concentrated solution. ○ The pressure causing water to move is
called osmotic pressure.
Hypotonic - Concentration of solute is higher in the cell, water
will be diffused into the cell.
○ Hypertonic - Concentration of solute is higher outside the cell,
water will be diffused out of the cell.
Active Transport
Movement of molecules from a low concentration to a high
concentration→ Against the concentration gradient ○ Requires
energy input.
○ Active transport requires a carrier protein that spans the membrane
to actively move chemicals from a low to a high concentration,
utilising cellular energy
Endocytosis
A particle is too large to pass
through the membrane, the membrane can change shape to surround
and engulf the particle.
○ Form vesicles in the membrane
○ Phagocytosis- Eating
○ Pinocytosis- Drinking
● Exocytosis
○ A process in which substances are transported to the external
environment of the cell.
○ Used for secreting proteins, removing waste and breakdown products
from the lysosomes.
Surface Area to Volume
○ Smaller cells = More efficient
○ The larger the cell becomes, the smaller the SA:V ratio, therefore
becomes less efficient to absorb nutrients
○ Smaller cells allow a faster movement of substances between the
center and surface of the cell → Less energy required
○ Cells may have elongated extensions to increase SA:V ratio to be
more efficient.
○ As the cell size continues to grow it reaches a point where
diffusion is not fast enough to sustain the cell, so the cell divides
if it’s possible.
○ Increasing SA:V ratio
■ Cell Compartmentalisation
Organelles live and work in separate areas.
Allows for more efficient movement because of more space
Reduces the amount of exchange between the membrane
■ Flattened Shape
Volume constant but increases surface area
Red blood cells
■ Membrane extensions
Works well for absorbing cells and secreting cells
Microvilli
Concept/Term
Meaning
Simple Diffusion
Does not require energy. Allows smaller molecules to easily move through the membrane
Facilitated Diffusion
Requires energy and is assisted by carrier proteins and channel proteins. Allows large molecules to pass through
Solute
what will be dissolved
Solvent
the liquid in which a solute is dissolved in. They will form a solution
Solution
is a mixture of two or more substances mixed together
Concentrated Solution
Is a solution that contains a large amount of solute compared to the amount that could dissolve
Dilute Solution
Dilution is decreasing the concentration of a solute in the solution. Occurs when mixing with more solvent.
Concentration Gradient
an area where particles move from high concentration to low concentration
Semi Permeable
allows certain substances to enter into the cell through the ‘semipermeable membrane’
Impermeable
Does not allow substances through the membrane
Selectively Permeable
the membrane only lets some materials through, by passive or active transport
Channel Proteins
used in passive transport
Carrier Proteins
used in active transport
Osmosis
Is the process in which water moves in and out of the cell, it does not need energy. Goes from high concentration to low concentration. Diffusion of water
Osmotic gradient
The difference in concentration between two solutions on either side of a semipermeable membrane.
Osmotic pressure
the pressure that is applied to a solvent to stop it from passing into a given solution by osmosis.
Isotonic solution
Two solutions that have the same osmotic pressure across the membrane
Hypertonic solution
When the concentration is greater outside the cell than inside
Hypotonic Solution
When the concentration isgreater inside the cell than outside
Active Transport
Moves from low concentration to high concentration against the gradient ; requires energy
Passive Transport
The movement of substances in and out of the cells without exerting energy
Endocytosis
Large particles that have to be moved into the cell, the membrane changes shape to let the particle in. type of active transport. turns into vesicle once inside the cell.
Exocytosis
moves materials out of the cell eg: waste. removes vesicle membrane
Vesicles
small structure in a cell which consists of fluid enclosed by a lipid bilayer. (membrane bubble)
Phagocytosis
‘cell eating’ when solid particles are engulfed
Pinocytosis
‘cell drinking’ when fluid is engulfed
Receptor-mediated
detectives specific molecules
Cell Requirements
Organic Compounds
○ Contain Carbon and Hydrogen → Protein, Vitamins, Carbohydrate
Inorganic Compounds ○ Water (H2O)
■ Important solvent and transport medium.
Oxygen (O2)
■ Needed for efficient energy supply from cellular respiration.
■ Taken in as gas or in solution.
○ Carbon Dioxide (CO2)
■ Ultimate source of carbon atoms for organic molecules.
○ Nitrogen (N2)
■ Key atom in the acids that make up proteins.
○ Minerals
■ Important for building enzymes and vitamins.
Biochemical Processes
Photosynthesis
Stage 1 → Light Stage
■ Photon from the sun enter the chlorophyll
■ The light is used to break down water into oxygen and hydrogen. ■
Oxygen is released into the atmosphere ■ Hydrogen is absorbed.