A1.1 - Water - IB Bio

Question 1

What physical and chemical properties of water make it essential for life?

Answer 1

Byoancy: The ability of an object to float, meaning it has a fluid to extert an upward force on an object. Many birds have hollow bones, which means they aren’t dense and the byoant force will hold them up. Also, seals have a large amount of blubber which makes them buyoant. Viscocity: Viscoity is a fluid’s resistance to objects passing through them. Water is more viscou than other substances like organic solvents and air because it can form hydrogen bonds within itself Thermal conductivity: This is the measure of a matireal’s ability to move heat across a temperature gradient. Water conducts and transfers heat more rapidly than air (water has greater thermal conductivity than air). For example, a seal is insulated with blubber to maintain body temperature - because the looj is mostly in air it does not loose much heat (as air has lower thermal conductivity). When in water the loon ensured it maintains its feathers well (ensuring they’re well oiled and feathers trap air) this ensures that they don’t lose too much heat in the wate.r High specific heat capacity: This is the quantity of heat needed to raise the temperature of a chemical per unit mass. Water the highest specific heat capacity, which makes it good for temperature regulation. This makes it a good habitat for aquatic animals (water must absorb a lot of energy before changing temperature) As seal are mostly aquatic the water temperature doesn’t change for them compared to a loon which are much more of a land animal.Cohesion: The sticking together/to each other’ of water molecules. This is important because it’s how water travels through the xylem in vascular plants. This process is known as transportation. The cohesive nature of nature gives it surface tension. The surface tension in turn allows organisms such as pond skaters to move across the surface. For pond skaters the surface of water is their habitat. The surface tension transmits vibrations from fallen invertebrates, allowing them to detect and locate their pray. Adhesion: This property occurs as a result of the polarity of water molecule and its ability to form hydrogen bonds. It’s when water molecules stick to other molecules that are charged or polar for similar reasons, that they stick together. Capillary action is caused by the combination of adhesive forces causing water to bond to surface, like the xylem. The capillary action is helpful in the movement of water during transportation and also when you drink using a straw. Again, individual hydrogen bonds are weak, but large number of bonds gives adhesive forces great strength. Solvent: Water can dissolve many organic or inorganic substances that contain electrongeative atoms like fluroine, oxygen and nitrogen. This is why it’s called the universal solvent. Most biochemical reactions take place in solution where water is the solvent. The cytoplasm is largely water and all cells exist in a medium which is water based like blood or a pond, The solubability of different molecules affects their mode of transport in living organisms. Eg. Glucose is a polar molecule which is why it’s freely soluble (carried by the blood plasma)

Question 2

What are the challenges and opportunities of water as a habitat?

Answer 2

Challenges: - oxegyn availability is low- sunlight is very low (aquatic animals still need the warmth of the sun and aquatic plants need it for photosynthesis, which is aquatic animal’s main food source)- climate change is changing the temperature of the water, making it challenging for non-thermoconformer organisms. - the challenges of density and viscosity for non-torpedo shapes organisms caused by malformation- habitat can be destroyed (e.g. pollution and climate change)Opportunities: - Easy to maintain body temperature- don’t have to look for water- torpido-shaped organisms can be efficiently - mass of organism is always supported, allowing high-mass animals to survive (wouldn’t survive out of water)- animals can modify density

Question 3

Why should we appreciate water?

Answer 3

The first cells originated in water and water remains the medium in which most processes of life occur.

Question 4

Why is water important?

Answer 4

• most organisms have high water content (75%-85%)- many organisms live in water- most chemical reactions of life take place in water - most life processes happen in water, in cytoplasm or surfaces of cells- the first cells originated in water

Question 5

What should we understand about the polarity of covalent bonding within water molecules?

Answer 5

The polarity of covalent bonding within water molecules is due to unequal sharing of electrons and hydrogen bonding due to this polarity occurs between water molecules. Leading to a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.The oxygen atom’s stronger electronegativity in water leads to charge separation, making it polar and capable of forming hydrogen bonds with other polar substances.

Question 6

What does polar mean?

Answer 6

Polar means a molecule (like water) has regions of slight charges due to the unequal sharing of electrons in a polar covalent bond. Oxegyen is stronger because it has a higher electronegativity causing it to carry a partial negative charge.

Question 7

What causes the covalent bonds between oxygen and two hydrogen atoms in water?

Answer 7

The nuclei of oxygen are significantly larger (because it has more protons) and greater (positive partial charge) than the hydrogen nuclei (+1). However, the oxygen attracts the electrons more strongly than the electron pair in the covalent bond is found ‘closer’ to the oxygen than the hydrogen nuclei.

Question 8

What effect does the covalent bonds between oxygen and two hydrogen atoms in water?

Answer 8

This creates a polar molecule in which the oxygen carries an additional small negative dipole and each hydrogen carries a small positive dipole.

Question 9

What happens due to the polarity of water molecules?

Answer 9

Due to the polarity of the water molecules, the small negative charge on each oxygen atom attracts the hydrogen atoms of other water molecules. - These attractions are called hydrogen bonds. - A hydrogen bond is water has a strength of 0.5 kcal/mol but these vary in strength based on the solution. - Hydrogen bonds can occur between water molecules and with other types of polar molecules. - The hydrogen bond does not change the chemical properties of water but does account for physical properties.

Question 10

How does adhesion and cohesion benefit living organisms?

Answer 10

• For the capillary action to occur both cohesion and adhesion need to occur.. For example, the capillary action can take place in the xylem of a plant. Cohesion occurs because water molecules are weakly attracted to each other via hydrogen bonds. Water is polar and the partial negative change on the oxygen atom in one water molecule attracts the hydrogen atom in a neighboring water molecule. Adhesion occurs because water molecules form hydrogen bonds with the xylem cell wall.

Question 11

Why do adhesion and cohesion act together?

Answer 11

Cohesion and adhesion work together to maintain the water column all the way from the root to the stomata. The rapid loss of water from the leaf pulls the water column stressing the cohesion and adhesion between water molecules. These properties create a suction effect or transpiration pull in the xylem.When water evaporated through the stomata of the leaf. adhesion causes water to be drawn through the cell wall from the xylem vessels in the veins of the leaf.Even though the pressure in the xylem of the leaves is low, the force of adhesion between the water molecules and the cell walls in the leaf is strong enough to suck the water out of the xylem further reducing the water pressure. The low pressure generates a pulling force known as the transpiration pull and it’s strong enough to pull water upwards against gravity to the top of the tallest tree. Transpiration is a passive process (with the only energy involved being heat energy which causes the evaporation of water at the leaf surface)

Question 12

How do solvent properties benefit living organisms?

Answer 12

Water is the solvent of blood, tissue fluid and the cytoplasm. Therefore, it allows the transport of the soluble minerals, carbohydrates, amino acids, etc. that are required to be transported around the body.

Question 13

When can you use coolant in your answer?

Answer 13

• lots of energy required to heat water- water has a high specific heat capacity- high hydrogen bonding of water molecules - when water evaporates energy is used- water cools organisms (sweating, panting, transportation)

Question 14

When can you use transport in your answer?

Answer 14

• water is polar- water is a universal solvent- water dissolves many organic and inorganic substances- the movement of water carries substances around an organism (eg. blood, phloem, xylem, adhesion, cohesion, and medium for external transport (eg. gametes)

Question 15

When can you use habitat in your answer?

Answer 15

• water is transparent- water allows light through for photosynthetic organisms- organisms live in/on/surface tension for surface creatures/buoyancy- water contains dissolved gases- fish/aquatic organisms survive under ice at the surface

Question 16

Quickly outline the thermal cohesive and solvent properties of water

Answer 16

• water has a high specific heat capacity- a large amount of heat causes a small increase in temperature- water has a high latent heat of vaporization- a large amount of heat energy is needed to vaporize/evaporate water- hydrogen bonds between water molecules make them cohesive/sick together- this gives water a high surface tension/why water rises up in xylem- water molecules are polar, which makes it a good solvent

Question 17

How did Earth get its water?

Answer 17

Earth formed around 4.5 billion years ago and it is thought water appeared around 4.4 bya. At present, asteroids up to a few hundred km across seem the most likely source of Earth’s water, specifically the types of asteroids that dominate the outer asteroid belt between Mars and Jupiter. - The distance of the earth from the sun keeps the temperature below that needed to vaporize water. The water stays in liquid/ice form due to cohesion between the water molecules (via hydrogen bonds)- earth’s gravity keeps water from escaping the planet.

Question 18

What is the habitability zone and why is it important?

Answer 18

• The Goldilocks Principle applies to the range of distances that a planet can be from its star and maintain surface temperatures that are just right for water to be liquid. This range is known as the Goldilocks zone. Temperatures that allow for liquid water are considered ‘just right’ because life as we know it requires water. - Based on the idea that liquid water on a planet’s surface makes life possible, the Goldilocks Zone if our solar system extends approximately from the orbit that Venus takes around the sun to the orbit that Mars takes around the sun. Earth’s orbit is within the sun’s Godilocks Zone. This is why Earth can maintain a vast ocean of liquid water, which makes Earth a place where life can thrive.