TERM I-II
, A1.1 UNITY AND DIVERSITY: MOLECULES:
WATER
A1.1.1-3: STRUCTURE OF WATER
● Explain that water is the substance in which cells first developed and life’s
processes still occur.
- Every cell has cytoplasm, which is made of water.
- Metabolism (chemical reactions of a cell) can only occur in the presence
of water.
- Plasma membrane (barrier between inside and outside of cell) only
functions in water.
● Explain how a difference in electronegativity between two atoms results in a
polar covalent bond.
- Electronegativity is how strongly an atom attracts the elements it shares
with another atom (in this case how strongly oxygen attracts the shared
electrons)
- Electronegativity is influenced by…
- # of protons in the nucleus of an atom: protons have a positive
charge so they will attract negatively charged atoms
- # of orbital levels of an atom: more orbital levels will decrease
the pull of the atom because the nucleus is shielded by orbital
levels
- Oxygen has more electronegativity than hydrogen, so it attracts more of
the shared electrons.
- When electrons are unevenly shared like this, it’s called a polar
covalent bond.
- Polar - having an uneven distribution of electrons
- Water is polar because as the shared electrons spend more time with
oxygen, oxygen becomes more electronegative than hydrogen, which
has a positive charge, creating a positive pole (hydrogen) and a negative
pole (oxygen).
● Draw two or more water molecules and hydrogen bonds between them with a
notation to indicate polarity.
,● Explain that water molecules are attracted to each other and that this property,
cohesion, has important impacts on organisms.
- Cohesion is the attraction of ‘like’ molecules. In this case, it is when
water molecules are attracted to other water molecules.
- Cohesion pulls water molecules together, and this force may counteract
gravity
- Vascular plants use cohesion to transport water up xylem tubes. The
water travels through the xylem from the root of the plant to the leaves,
and as it does so, cohesion attracts more water molecules and takes them
up the xylem as well.
- Water striders can walk on the surface of water because of its water
tension. The water molecules pack closely together because of the
properties of cohesion, which creates the water tension necessary for the
water striders to walk on water.
● Explain why water forms hydrogen bonds
- Oxygen is partially negative, and hydrogen is partially positive. Because
of this, an intramolecular force holds water molecules together, called a
hydrogen bond. The charges are partial, therefore the bond is weak.
● Distinguish between cohesion and adhesion
- Cohesion is the attraction of water molecules to other water molecules
, - Adhesion is the property of water which makes it stick to other surfaces.
A1.1.4-5: INTERACTIONS WITH WATER
● Explain how the properties of water affect its roles as a means of transport.
- Cohesion and adhesion make capillary action possible. Capillary
action is when water travels through narrow spaces. It happens when
adhesion is greater than cohesion.
- A meniscus is provided by capillary action (curved top of water when
reading a measuring tube.
- Plants use capillary action to move water into cell walls. When water is
pulled up the xylem, the cellulose fibers pull water between them
- When water evaporates from a leaf, capillary action sends the lead more
water so it doesn’t dry out
● Explain how the solvent properties of water are linked to its role as a medium
for metabolism.
- Hydrophilic molecules are attracted to water, while hydrophobic
molecules repel water.
- Hydrophilic molecules are typically polar and can therefore dissolve in
water
- Like dissolves like: polar solvents like water dissolve polar materials,
and non-polar solvents like belzene dissolve nonpolar substances.
- The substrates and enzymes that catalyze them are usually in the
cytoplasm, which is watery.
- The way the enzymes interact with water is integral to the cells
composition
- The hydrophobic part of the cell membrane forms a barrier between the
inside and outside of the cell.
- Aquaporins (transmembrane proteins) have a hydrophobic exterior and
a hydrophilic exterior, which allows water to move through the cell.
- Solvent properties allow animals to transport materials from cell to cell.
Animals use blood or haemolymph to do this, both of which are water
based.
- Plasma is the liquid portion of blood in which materials are dissolved.
- Some materials like oxygen are non-polar and cannot be dissolved by
water, so they have to be bound to and carried by hemoglobin.
● Explain how the cohesive and adhesive properties of water are linked to its role
as a medium for transport in plants and animals.
, A1.1 UNITY AND DIVERSITY: MOLECULES:
WATER
A1.1.1-3: STRUCTURE OF WATER
● Explain that water is the substance in which cells first developed and life’s
processes still occur.
- Every cell has cytoplasm, which is made of water.
- Metabolism (chemical reactions of a cell) can only occur in the presence
of water.
- Plasma membrane (barrier between inside and outside of cell) only
functions in water.
● Explain how a difference in electronegativity between two atoms results in a
polar covalent bond.
- Electronegativity is how strongly an atom attracts the elements it shares
with another atom (in this case how strongly oxygen attracts the shared
electrons)
- Electronegativity is influenced by…
- # of protons in the nucleus of an atom: protons have a positive
charge so they will attract negatively charged atoms
- # of orbital levels of an atom: more orbital levels will decrease
the pull of the atom because the nucleus is shielded by orbital
levels
- Oxygen has more electronegativity than hydrogen, so it attracts more of
the shared electrons.
- When electrons are unevenly shared like this, it’s called a polar
covalent bond.
- Polar - having an uneven distribution of electrons
- Water is polar because as the shared electrons spend more time with
oxygen, oxygen becomes more electronegative than hydrogen, which
has a positive charge, creating a positive pole (hydrogen) and a negative
pole (oxygen).
● Draw two or more water molecules and hydrogen bonds between them with a
notation to indicate polarity.
,● Explain that water molecules are attracted to each other and that this property,
cohesion, has important impacts on organisms.
- Cohesion is the attraction of ‘like’ molecules. In this case, it is when
water molecules are attracted to other water molecules.
- Cohesion pulls water molecules together, and this force may counteract
gravity
- Vascular plants use cohesion to transport water up xylem tubes. The
water travels through the xylem from the root of the plant to the leaves,
and as it does so, cohesion attracts more water molecules and takes them
up the xylem as well.
- Water striders can walk on the surface of water because of its water
tension. The water molecules pack closely together because of the
properties of cohesion, which creates the water tension necessary for the
water striders to walk on water.
● Explain why water forms hydrogen bonds
- Oxygen is partially negative, and hydrogen is partially positive. Because
of this, an intramolecular force holds water molecules together, called a
hydrogen bond. The charges are partial, therefore the bond is weak.
● Distinguish between cohesion and adhesion
- Cohesion is the attraction of water molecules to other water molecules
, - Adhesion is the property of water which makes it stick to other surfaces.
A1.1.4-5: INTERACTIONS WITH WATER
● Explain how the properties of water affect its roles as a means of transport.
- Cohesion and adhesion make capillary action possible. Capillary
action is when water travels through narrow spaces. It happens when
adhesion is greater than cohesion.
- A meniscus is provided by capillary action (curved top of water when
reading a measuring tube.
- Plants use capillary action to move water into cell walls. When water is
pulled up the xylem, the cellulose fibers pull water between them
- When water evaporates from a leaf, capillary action sends the lead more
water so it doesn’t dry out
● Explain how the solvent properties of water are linked to its role as a medium
for metabolism.
- Hydrophilic molecules are attracted to water, while hydrophobic
molecules repel water.
- Hydrophilic molecules are typically polar and can therefore dissolve in
water
- Like dissolves like: polar solvents like water dissolve polar materials,
and non-polar solvents like belzene dissolve nonpolar substances.
- The substrates and enzymes that catalyze them are usually in the
cytoplasm, which is watery.
- The way the enzymes interact with water is integral to the cells
composition
- The hydrophobic part of the cell membrane forms a barrier between the
inside and outside of the cell.
- Aquaporins (transmembrane proteins) have a hydrophobic exterior and
a hydrophilic exterior, which allows water to move through the cell.
- Solvent properties allow animals to transport materials from cell to cell.
Animals use blood or haemolymph to do this, both of which are water
based.
- Plasma is the liquid portion of blood in which materials are dissolved.
- Some materials like oxygen are non-polar and cannot be dissolved by
water, so they have to be bound to and carried by hemoglobin.
● Explain how the cohesive and adhesive properties of water are linked to its role
as a medium for transport in plants and animals.
