SL Bio Unit 2

What is the structure of water

One atom of oxygen with two atoms of hydrogen through covalent bonds. Has a V-shape due to unshared electrons on oxygen which creates a polar molecule with a partial negative charge near the oxygen atom and a partial positive charge near the hydrogen atoms. Polar molecule because of the unequal sharing.

What is a hydrogen bond and what is the strength

The positively charged hydrogen is attracted to the negatively charged oxygen of nearby water molecules. Creates a force called hydrogen bond which forms between two water molecules or between a water molecule and another type of charged ion or atom. It is weaker than a covalent bond, but a high number of hydrogen bonds are strong enough to hold water molecules together as liquid.

What is cohesion of water molecules

When hydrogen bonding between water molecules holds them together in a network. These bonds continually break and reform with surrounding water molecules.

Explain transpiration using cohesion

Cohesive forces allow water molecules to be drawn up xylem vessels by water evaporation from the leaves. Water evaporates through stomata under the surface of a leaf (transpiration). The transpiration will create a low pressure area in the leaf. The polarity of water molecules pulls the entire water column to move towards the low pressure area. The xylem tube within the leaf is continuous with the xylem in the stem and root, so the water moving upwards is replaced by ground water moving into the root system.

Explain surface tension with cohesion

At the surface of water where it meets the air, there is a greater attraction of water molecules to one another than to the air, which forms a strong surface. The strong surface allows some small organisms to walk on water.

What is adhesion of water molecules

Where individual water molecules cling to surrounding materials and surfaces. Water adheres strongly to most surfaces and are drawn up long columns (e.g. xylem in plant stems).

What is capillary action

If the adhesive force to the side of a narrow tube is stronger than the cohesive force, water will be drawn upwards against the pull of gravity

What is a meniscus

When adhesion of water to the sides of a tube or container creates an upward force on the edges of the liquid, causing the surface to curve

Explain transpiration using adhesion

Water molecules adhere to the cellulose in the xylem through hydrogen bonding. Water molecules adhere to the cellulose in the xylem through hydrogen bonding. Prevents the water column from breaking. The walls of plants are cellulose and it is polar which allows water to adhere to it. Cell walls can draw water up through capillary action.

What is capillary action in soils

Soil has many vertical thin channels known as capillary tubes in which plant roots are located. When water enters capillary tubes, adhesion between water molecules and the wall of the capillary draws water up the small tube. This is used by plants to bring water up from the water table to their roots when the ground becomes dry

How to dissolve a solute

The hydrogen bonds between water molecules must break and the bonds between the solute particles must also break. The water molecules then surround the solute particles and if water molecules are surrounding an ion, then ion-dipole forces are formed. If water molecules are surrounding a charged molecule, then new hydrogen bonds are formed.

What is the solubility of CO2, O2, and N2

CO2 is slightly soluble because it undergoes a series of chemical reactions to form HCO3. O2 and N2 have low solubility because they are non-polar

What are the physical properties of water

buoyancy, viscosity, thermal conductivity, specific heat capacity

What is specific heat capacity for water and give example of how it benefits animals

The amount of energy required to raise the temperature of 1kg of substance by 1 degree celsius. Water has a high specific heat capacity meaning it takes a lot of energy to raise the temp. The high specific heat capacity prevents large fluctuations in temperature which provides a cushion for the animals. Aquatic environments are very slow to change and have more stable temperatures than terrestrial environments. Air has a lower specific heat capacity and so it causes the water at the surface to freeze and provide a platform for marine animals (like seals) to live on.

What is thermal conductivity

The measure of how easily heat flows through a specific type of material. Water has a higher thermal conductivity than air, so water is better at conducting heat. Feather can be used to trap a thin layer of air to reduce exposure of air to skin to maintain body temperature. A layer of ice can also provide insulation because of its low thermal conductivity. Ice can trap thermal energy in the water beneath, and increase the ocean temperature.

What is buoyancy

Buoyancy is the vertical force provided by any fluid when an object is placed on or in it. Aquatic diving animals change their buoyancy when underwater. Birds like loons can squeeze air out of their lungs to decrease buoyancy. Subcutaneous fat in seals can provide the necessary buoyancy when underwater.

What is viscosity

Viscosity is a fluid’s resistance to flow, and water is more viscous than air, so bird plumage is adapted to hold and deflect air to make it easier to achieve flight. The light feathers can move through the air easily with minimal friction. In water, molecules of water below the surface move past each other easily which shows low viscosity. Therefore, to achieve movement in water there must be resistance against the water. Loons achieve this with the use of webbed feet, while marine animals like seals use their flippers to propel themselves.

What is the origin of water on earth

Most scientists believe that water originated outside of earth and it came from studying asteroids and meteorites which carry water and amino acids. These meteorites crashed into the earth and could have provided a source of water.

What are the necessary conditions for extraterrestrial life

Any plant with water and similar to earth that allows for liquid water. Cannot be too close or far from the sun, and this is known as the goldilocks zone. Also has enough gravity to retain water. Earth also has an atmosphere and magnetic field that protects it from harmful radiation emitted from the sun. There are around 1800 planets beyond our solar system, and out of those there are only 16 in each of their star’s goldilocks zone.

How do scientists look for extraterrestrial life

They use transit spectroscopy so as a planet passes in front of their nearest star, light passes through the planet’s atmosphere. The light is analyzed to determine which wavelengths are being absorbed or deflected.

What are the four organic molecules

Carbohydrates, lipids, proteins, and nucleic acids

What is a covalent bond

Sharing valence electrons

What is an ionic bond

Gaining or losing electrons

Which organic molecules can form double bonds

Carbon atoms can form more than one bond between them. Carbon atoms can also share 2 pairs of electrons to form a double bond. They can also form a double bond with nitrogen and oxygen.

What is a functional group

A specific group of atoms within a molecule that is responsible for characteristic chemical reactions. Functional groups determine the properties and behaviors of organic compounds. Many biological molecules have functional groups containing carbon bonded to oxygen.

How are macromolecules produced by condensation reactions that link monomers to form a polymer

Macromolecules are produced by condensation reactions that link monomers (individual networks of atoms or molecules) to form a polymer. Examples include polysaccharides, polypeptides, and nucleic acids. The subunits of monomers create a chain called a polymer. In each case, the chemical process that links another monomer on to the end of the polymer is a condensation reaction.

Give example of how do less soluble molecules dissolve in water

Oxygen is low solubility and requires assistance by combining with haemoglobin, and then more oxygen will be carried directly in the bloodstream. Oxygen is less soluble at body temperature (37C) than 20. It is sparingly soluble but soluble enough for dissolving in oceans, rivers, and lakes for aquatic animals to breathe. Haemoglobin binds with oxygen to allow sufficient oxygen to be transported.

How do you draw a hydrogen and covalent bond

With a dotted or dashed line and covalent is straight line

How do enzymes react in water

Enzymes require water to hold shape and stability, and enables them to catalyse reactions in aqueous solutions. Hydrogen bonds will often facilitate the binding of the enzyme active site and the substrate which forms an enzyme substrate complex.

What is DNA

Deoxyribose nucleic acid carries genetic code for all living organisms. DNA is mainly found in the nucleus and also in chloroplasts and mitochondria.

What is RNA and give examples of viruses with RNA

Main component of ribosomes that play an important role in protein synthesis. Viruses like SARS-CoV-2 contain RNA instead of DNA that causes a variety of diseases such as COVID-19, ebola, influenza.

What is DNA and RNA made of

Polymers made up of many repeating units. Each nucleotide has a pentose sugar, organic base, phosphate group.

What is the bond between base and phosphate group to the sugar

Covalent bond

Which bases are purine and pyrimidine

Adenine and Guanine are purine
Cytosine, thymine (in DNA), and uracil (in RNA) are pyrimidine

Which nitrogenous bases are paired together

Cytosine and Guanine (3 hydrogen bonds)

Thymine and Adenine (2 hydrogen bonds)

In RNA thymine is replaced by uracil so then uracil is paired with adenine

What kind of bond is between the bases

Hydrogen bond

What is polynucleotide

When the phosphate group of one nucleotide forms a covalent bond to the pentose sugar of the next one and creates a large polymer. These polymers form nucleic acids which are also polynucleotides

What is a condensation reaction and give example

When two molecules are combining into a larger molecule while water is released. The phosphate group of one nucleotide is linked to the pentose sugar of the next one by condensation.

What is mRNA

messenger RNA is formed in the nucleus and transported to the ribosome in the cytoplasm

What is tRNA

Transfer RNA is responsible for transporting amino acids to ribosomes during protein synthesis

What is rRNA

Ribosomal RNA is what forms parts of ribosomes

What is the structure of DNA

A double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding. It is a polynucleotide because it is many nucleotides together in a long chain. One strand has the 5’ to 3’ strand and the other is the 3’ to 5’ strand.

What does it mean that genetic sequence is highly conserved

The same across many groups of organisms

What is the sugar-phosphate backbone

When the phosphate group of one nucleotide forms a covalent bond to the pentose sugar in the next nucleic acid polymer

What is the sugar in RNA and DNA

In RNA is ribose and DNA is deoxyribose

What is the 3D shape of DNA

Double helix

What determines the complementarity of base pairs in base pairing

Hydrogen bonds

What is a coding strand

One of the strands of a DNA molecule will carry the base sequence that will be read by enzymes

Does the order of the bases matter

Yes, it will determine the order of amino acids in the proteins that are synthesised during protein synthesis, thus affecting the protein's structure and function.

What is a codon

The code is read as triplets of bases, and every sequence of three bases will code for one amino acid. The sequence of amino acids will determine the shape and function of the protein.

What does it mean that the genetic code is universal

Almost every organism uses the same code. Provides evidence for a universal common ancestor where all living organisms on Earth evolved.

What is a coding sequence

Base sequences that form parts of regions of codes for proteins

What is a non-coding sequence

Base sequences that are in regions that doesn’t code for proteins

What is the composition of eukaryotic chromosomes

DNA bound to histone proteins

What is the function of the rER

Protein synthesis and protein transport

What is the function of the sER

Lipid synthesis, production of sex hormones, calcium ion storage