Processes of Life: How big can a cell get

First, we did an experiment on osmosis and diffusion.

1. Cut paper towels into 3 strips of about 30 x 20mm and soak them in cabbage juice (which is purple)
2. Cut your agar block (which has been soaked in cabbage juice) to the following dimensions
a. 3 pieces of 5 x 5 x 5 mm
b. 3 pieces of 5 x 5 x 20 mm
c. 3 pieces of 10 x 10 x10 mm
3. Immerse one of each dimension into the following solutions:

• 7 up
• Lemon
• Soap

4. Introduce a few drops of each of your 3 solutions onto a different strip of the cabbage juice soaked paper towel
5. Observe the colour change
6. Transfer 2cm^3 of each of the solution into separate test tubes. Add an equal volume of cabbage juice to each of these test tubes and record the colour change

Rate of Diffusion in different sizes of Agar

Agar Block	5 x 5 x 5mm	5 x 5 x 20mm	10 x 10 x 10mm
Surface Area (cm^2)	150	450	600
Volume (cm^3)	125	500	1000
Surface Area: Volume ratio	6:5	9:10	3:5
TIme for agar block to change colour completely (min)	20s	10s	1.10

Colour change of cabbage juice in a different medium

		7 up	Lemon Juice	Soap
Agar	Initial Colour	Purple	Purple	Purple
	Final colour	Slightly lighter purple	Pink	Blue
Paper towel	Initial Colour	Blue	Blue	Blue
	Final Colour	Light purple	Pink	Blue
Liquid	Initial colour	Colourless	Yellow	Yellowish

                       Final Colour     Light Purple               Pinkish-Orange  Light Purple

From this data, I can conclude that the higher the surface area to volume ratio, the faster the rate of diffusion.
There is a cap on the maximum size of a living cell as if the size of a living cell is too high, there will be a low surface area to volume ratio, causing inefficient diffusion.
The cell's surface area to volume ratio affects the rate of diffusion, which depends on the function of the cells. For example, the protusions on the large intestine increases the surface area and nutrients absorbed by the large intestines.

Osmosis and Diffusion (Experiment)

Today we did 3 experiments on Osmosis and Diffusion--
1. Osmosis in Plant tissues
2. Demonstration of Osmosis Processes in Non-living System Using an Osmometer
3. Osmosis in Plant cells

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1. In the first one, we used 3 potato strips of around 50 mm each.
We placed each one in different solutions, and found that Strip A increased in length, and Strip B and C decreased in length.
In the case of Strip C it was because the water molecules moved from a region of higher water potential (strip C) to a region of lower water potential (Solution) through a partially permeable plasma membrane. Thus the water potential in the Potato Strip decreased as the water molecules moved out of the cell and it became shorter.

2. In the second experiment, we observed two thistle funnels with cellophane paper tied over the mouth, and placed in a beaker.
Both the beakers were filled with distilled water. One thistle funnel has 50% sucrose solution, and the other with only distilled water.
After thirty minutes, the thistle funnel with sucrose solution in it had a higher water level.
This was because water molecules from there was a net movement of water molecules from the distilled water to the solution inside the funnel through the cellophane paper.

3. In the third experiment, we prepared a slide of a Hydrilla leaf. We observed it

Hydrilla leaf under 40x

Then we put it in saline solution

Hydrilla leaf in salt solution after 15 minutes

Osmosis, Diffusion, Water potential

Water potential 

• must be used in comparison with two environments 
• Refers to the tendency to donate water molecules
• e.g. if liquid A has a lower concentration than liquid B, you can say the liquid A has a lower water potential as compared to liquid B (or vice versa).
• Water molecules always move from a region of higher water potential to a region of lower water potential

Osmosis

e.g [water moving to a hair root cell]

• Net movement of water molecules from a region of high water potential to a region of low water potential across a partially permeable membrane


• The cells will shrink in size. If it lasts for a prolonged period of time the cell will die 
• Animals cells: known as crenated 
• Plasma has a lower potential compared to the cytoplasm of the cell so osmosis occurs and the water will be transferred to the cytoplasm. However, there is a limit to how much the cytoplasm can expand. When that limit is reached, the cell will burst.
• Cell wall (plant cells) prevent the cell from expanding, as such the plant cell does not burst

When you get a question on osmosis, remember to write out the definition of osmosis

Net movement: There may be forces exerted in different directions but the most (strongest/ stronger) force is exerted towards is the net movement.

Diffusion

e.g. [tea bag flavouring to water] 

• The movement of particles within a gas or liquid
• From a region of high concentration to a region of lower concentration (down a concentration gradient)
• Until an equilibrium is reached

The difference between osmosis and diffusion is that osmosis requires a partially permeable membrane and is applicable only to water molecules.

How do you explain this?

1. State that osmosis is occuring 

• Osmosis occurs because the surrounding solution has a lower water potential than the cytoplasm of the cell. Because of this difference in water potential, there is a net movement of water molecules from the cytoplasm of the cell across the plasma membrane to the surrounding solution. 

2. relate the defintion to the movement to the water molecules 

• The loss of molecules from the cytoplasm of the cell will lead to the decrease in volume of the cytoplasm of the cell

How do you explain this?

• Osmosis occurs. 
• Because the surrounding water solution has a higher water potential compared to the cytoplasm of the cell, there is a net movement of water molecules from the surrounding solution across the plasma membrane of the cell into the cytoplasm of the cell. 
• This will then lead to an increase in the volume of the cytoplasm of the cell. 
• If the cytoplasm of the cell continues to increase in volume, the animal cell will eventually burst or lyse. and when that happens, the cell dies. Moving down/ along the concentration gradient

PLANT CELL
If replaced with a plant cell with higher water potential than cytoplasm of cell,

• Because of the difference in water potential, 
• there is a net movement of water molecules across the plasma membrane into the cytoplasm of the cell
• There will be an increase in the volume and size in the cell and the cytoplasm will push against the cellular cell wall.
• The cytoplasm is exerting a pressure, known as turgor pressure, on the cell wall. This cell is now turgid (this term is only applicable to PLANT CELLS). Animal cells can be described as firm.

CELLS

CELLS

Cells:

• Prokaryotes 
• (Eg. Bacteria) absence of membrane bound organelles (any organelles in a cell that is surrounded by a membrane)

• Eukaryotes 
• (Eg. Animal and plant cells) presence of membrane bound organelles

Membrane bound organelles

Cytoplasm= cytosol + organelles within it

Eukaryotes:

Nucleus

membrane bound organelle that contains genetic material of cell DeoxyriboNucleic Acid (DNA)

↪ heredity

↪ direct cell activities

Chromosomes:

Chromosomes are compact structures into which DNA are organised. Contains proteins known as histones (basic protein)

Plasma membrane

To contain cytoplasm within the cell

Regulate/ control substances entering/ leaving the cell

This whole thing is a phospholipid bilayer. WHich means to say the cell membrane is a phospholipid bilayer. O.O

Lipid- Stands for what we know as FATS. Lipids consist of oil and fats.

Alcohol can be used to kill the lipid stuff in the membrane, which is why hand sanitizer is effective against bacteria

Membranes are partially permeable

semi-permeable ✘

selectively permeable ✘

Mitochondria

• Site of respiration.
• Breaks down the carbohydrates to monosaccharides.

Ecology and Taxonomy

Bio Lesson 25 July: Ecology

ECOLOGY

is the study of how living things interact with each other and with their environment.

Things are interconnected with one another in one way or another.

Environment consists of non-living (Abiotic) and living (Biotic) factors

Biotic Factors:

• Living stuff

Abiotic Factors:

• Air composition, sunlight, etc. light
• affects many living organisms, not just plants
• Temperature
• affects physiological activities of all living organisms
• Water
• essential for life.
• organisms may have specially adapted features for survival in places with a lot of or very little water
• primary source of energy → the SUN

TAXONOMY

Binomial nomenclature

• a two part scientific naming system, consisting of
• genus ( includes one or more physically similar species)
• species
• is always written in Italics

e.g.

Written as:

Homo sapiens

↓ ↓

Genus  Species

Linnaeus’ classification system

• has seven levels
• Kingdom (e.g. Animalia), 
• Phylum(e.g. Chordata), 
• Class(e.g. Mammalia), 
• Order(e.g.Primates), 
• Family(e.g. hominidae), 
• Genus (e.g. Homo), 
• Species (E.g. Homo Sapiens)
• Levels get increasingly specific from kingdom to species 
• The creatures in each level are included in the level above it

Have to be able to identify order.

Questions that may beasked: Can you name organisms that have a common order?

E.g. bobcat, lion, shaggy mane mushroom.

Example:

	Bobcat	Lion	Shaggy mane mushroom-cat
Kingdom	Animalia	Animalia	Fungi
Phylum	Chordata	Chordata	Basidiomycota
Class	Mammalia	Mammalia	Homobasidiomycetae
Order	Carnivora	Carnivora	Agaricales
Family	Felidae	Felidae	Copricaceae
Genus	Lynx	Panthera	Coprinus
Species	Lynx rufus	Panthera leo	Coprinus comatus

This system has its limitations:

• ** Linnaeus taxonomy does not account for molecular evidence.
• Linnaean system based only on physical similarities
• e.g. Family: Canidae put together because of physical similarities
• physical similarities are not always the result of close relationships
• Genetic similarities more accurately show evolutionary relationships

Do note that Classification is always a work in progress

THE TREE OF LIFE

• shows our most current understanding
• There are 6 Kingdoms
• Animalia,
• Plantae, 
• Protista, 
• Archaea, 
• Bacteria, 
• Fungi
• The three domains in the tree of life branch into the six kingdoms.
• Bacteria
• Bacteria kingdom
• includes prokaryotes in the kingdom bacteria
• one of the largest groups on earth
• classified by shape, need for oxygen, and diseases caused

• archaea 
• Archaeal kindom
• and eukarya
• Protista Kingdom
• Domain Eukarya branches into the Protista Kingdom

Then the tree of life branches off into the Animalia, Plantae and Fungi kingdoms.

modern taxonomy

6 kingdoms

- more traditional

- based on morphological characteristics, eg

-major cellular structure,

-methods of obtaining nutrients

-metabolism

-3 domains

derived from molecular biology

(not impt.) based on comparing sequences of ribosomal RNA to determine common ancestry

What you need to know:

Key concept

The current tree of life has three domains (Bacteria, Archaea, Eukarya)

-All living things bear scientific names that use the binomial signature (two parts, reflecting its genus and species)

- Linnaeus Classification System: Seven levels (need to remember all seven)

- Linnaeus taxonomy does not account for molecular evidence.

- Interpret data given from this classification system

- There are six kingdoms and (preceding that) 3 domains

- Domain Bacteria branches into the Bacteria kingdom

- Domain Archaea branches into the Archaeal kingdom

- Domain Eukarya (all eukaryotes) branches into the Protista Kingdom

- Then the tree of life branches off into the Animalia, Plantae and Fungi kingdoms.

- NOT required to memorize the scientific names of various organisms

- Classification of living things is a work in progress

- Living things cannot exist alone, there must be a relationship between them.

- Living things are adapted to the environment where they live. (impt for ecology)

- Ecology is the study of how living things interact with each other and with their environment.

- Abiotic factors & biotic factors

NOTES: Mr D will go through the rest of ecology next week to prepare for the FA.

Key Concept: Organisms can be classified based on physical similarities (what can be observed from these living things)

                       Such as whether they live in water, on land, or float in the air sleeping.

Classification and Diversity

Linnaeus developed the scientific naming system still used today, known as the Binomial Naming System/Nomenclature

Practical- Cells

Task for cell practical:
Procedure:
1. Place the prepared slide of a Human cheek cell (w.m.) on the microscope stage. Make the necessary adjustments to the microscope so that the cells can be seen clearly. These may be harder to find because they usually are either single or in small clumps. The cells look like pieces of a broken plate.
2. Draw and label 2 whole cheek cells from your slide. Label only the cell membrane, cytoplasm and nucleus.
3. Repeat with plant cell, but label cell wall too.

Cheek cell

Plant cell

Close up of plant cell: Little dot is the nucleus

Microscopy

Today for Science we learnt how to use a microscope.

Arm: Supports the body tube and is the part that you can grasp to carry the microscope. Pick up your microscope by its arm, keeping it upright, and supporting it underneath with your free hand. Set it gently on your lab desk.
 Base: Gives the microscope a firm, steady support.
Ocular lens (Eye piece): Magnifies ten times (l0x). This lens is often unattached, and thus it may fall out unless the microscope is kept upright.
Objectivelens:Magnifies the object by the factor marked on the particular lens. Low power (l0x) gives the smallest image, high power gives a large image (40x), and oil immersion gives the largest image (l00x). Sometimes a very low power scan objective (4x) replaces the oil immersion lens. *Objective lenses are always used in order: low, high, oil immersion.
Nosepiece: The revolving part to which objectives are attached. It must be firmly clicked into position when the objective is changed. Rough treatment can cause it to snap off.
Body tube: Joins the nosepiece to the ocular lens.
Stage: Supports the slide that is held onto it by stage clip, and has a hole so that light can shine up through the specimen. Always centre the specimen over this hole.
Coarse adjustment: Moves the body tube or stage up and down, depending on the design of the mi- croscope, to approximately the right position so that the specimen is in focus. This knob is used only with the low power.
Fine adjustment : Moves the body tube (or stage) up and down to precisely the right position so that the specimen is perfectly in focus. Use it to achieve fine focus with the low power objective and for all focusing with the high power and oil immersion objectives.
Light source: Usually a small electric light beneath the stage that is controlled by a push-button light switch. Sometimes a mirror is used to reflect light from another source into the microscope.
Iris diaphragm: Regulates how much light goes through the specimen. It is controlled by a lever that is moved back and forth.
Condenser: A lens located above the diaphragm which concentrates the light before it passes through the specimen. Its position is controlled by a knob on microscopes in which it is adjustable

First we viewed a letter cut out from a newspaper under a microscope, and found that it became upside down and inverted.

We then repeated the experiment, but with strings instead.

We then looked at cheek cells and plant cells.

Note: Elaboration on cells in next post