Final IB SL Biology

Define a population

A group of organisms of the same species living in an area at one time

Give two methods of estimating population size

Sampling, capture-mark-release-recapture

What is sampling used to investigate?

Abundance and distribution of populations

Give two types of sampling

Random and systematic

When is random sampling the best choice?

When a sampling area is reasonably uniform

How is random sampling done?

Lay out a grid over area to be studied, generate random number coordinates, place sample sites in coordinates

What assumption does a population estimate based on sampling make?

Individuals are distributed evenly across the site

What is used to study distribution of sessile organisms?

Quadrats

Give four types of data that can be recorded from a frame quadrat

Presence or absence of a species, species frequency, species abundance, percentage cover

What is used to study distribution of motile organisms?

Capture-mark-release-recapture

Describe capture-mark-release-recapture

The first large sample is taken and individuals are counted and marked in a way that won't affect their survival. The marked individuals are returned to their habitat and allowed to randomly mix with the rest of the population. After sufficient time, another large sample is captured, and the number of marked and unmarked individuals are counted. The proportion of marked to unmarked individuals is used to calculate an estimate of population size using the Lincoln index.

Lincoln index formula

M x N/R M = initial marked N = total in second sample R = marked in second sample

Give the four assumptions the Lincoln index makes

The marked individuals disperse and mix back in fully with the population. The marking doesn't affect survival rates. The marking doesn't rub off. The population stays the same size.

Define carrying capacity (K)

The maximum number of individuals of a species that an ecosystem can support

Give three abiotic factors affecting carrying capacity

Light availability, temperature, soil mineral availability

Give three biotic factors affecting carrying capacity

Competition for resources, predation, disease

Density-dependent factors act on a ? feedback effect

Negative

Give an example of a predator-prey interaction affecting population

Canada lynx and snowshoe hare

Give two types of population control factors

Top-down or bottom-up

What type of population control is limitation by predators?

Top-down

What type of population control is limitation by availability of resources?

Bottom-up

Give two ways interspecific competition strategies work

Increasing survival chances of species (eg camouflage) or decreasing survival chances of competing species (eg allelopathy)

What is allelopathy?

Chemical inhibition of another species' growth by secreting secondary metabolites that harm other organisms

Give an example of a plant species that carries out alleloapthy

Garlic mustard producing sinigrin reducing seed germination and root growth in other plant species

Explain how antibiotic secretion functions as allelopathy

Some microorganisms secrete antibiotics to kill bacteria, reducing interspecific competition

Give the three phases of the sigmoid growth curve

Exponential (logarithmic), transition, plateau

What happens in the exponential phase of the sigmoid growth curve?

No factors that limit population growth, so population increases exponentially as number of individuals and rate of growth increases

What happens in the transition phase of the sigmoid growth curve?

Limiting factors start to act, so rate of growth slows even though population is still increasing

What happens in the plateau phase of the sigmoid growth curve?

Limiting factors cause death rate to equal birth rate so population growth stops at carrying capacity, although still fluctuates

Give two organisms used to model the sigmoid growth curve

Yeast, duckweed

Explain how yeast is used to model the sigmoid growth curve

Yeast is grown in a broth culture, an the turbidity of the suspension is used to estimate the number of cells by measuring how much light can pass through at fixed time intervals with a turbidity meter or a colourimeter.

Explain how duckweed is used to model the Sigmoid growth curve

Place a small number of duckweed fronts into a petri dish containing distilled water and liquid fertiliser in a brightly lit location. Record the number of fronds present each week for six weeks.

Why is duckweed ideal for modelling population growth?

Reproduces quickly and asexually, and is easy to count as in clusters.

Give the two types of intraspecific interactions

Cooperation adn competition

Give three examples of intraspecific cooperation

Orcas hunt together by creating a wave to wash seals into the water, meerkats have roles within the group, ants work together to build nests and find food

Give three examples of intraspecific competition

Male red deer fight for mating, robins defend territorially, oak trees compete for light, water, and minerals

Define a community

Multiple populations of different species living and interacting in the same area

Give six interspecific interactions

Herbivory, predation, interspecific competition, mutualism, parasitism, pathogenicity

Give an example of parasitism

Fleas on dogs feeding on blood

Give an example of pathogenicity

Dutch elm disease is caused by a fungal pathogen that causes elm trees to lose their leaves and die

Give an example of mutualism

Zooxanthellae and coral polyps

Explain the symbiotic relationship between zooxanthellae algae and coral polyps

Polyps have tentacles which contain the zooxanthellae cells, providing shelter and protection for the algae, while the algae carry out photosynthesis and produce carbon compounds

Define an invasive/alien species

A species moving into an ecosystem where it was previously unknown

Why does the population of invasive species rapidly increase?

No natural population controls eg no natural predators or competitors

Give three ways an invasive species can affect an ecosystem

Competition with native species in a similar niche, decline in prey species, introduce new diseases which native species have no natural immunity to

Give an example of an invasive species

Grey squirrels from North America in the 1800s in the UK, largely outcompeting red squirrels in interspecific competition

Define endemic species?

Species found naturally in only one geographic area and no place else

Why are endemic species especially vulnerable to the effects of invasive species?

Local extinction is entire extinction

Why are enzymes necessary? Give two reasons

Most reactions occur slowly, and this isn't fast enough to sustain life, so enzymes act as biological catalysts. Also, the reactants would need to collide at the correct angle and speed, the chance of which is very low without enzymes.

Define metabolism

All of the chemical reactions that take place within cells and organisms

Define a metabolic pathway

A series of interlinked metabolic reactions

What are enzymes?

Globular proteins, specific to a substrate that act as biological catalysts to increase the rate of reaction

Which two things are complementary in an enzyme-substrate complex?

Chemical properties and shape

What do anabolic reactions do?

Build large molecules from smaller ones

Give three examples of anabolic reactions

Photosynthesis, protein synthesis, glycogen formation

What type of reactions do anabolic reactions often include?

Condensation reactions

Are anabolic reactions endergonic or exergonic?

Endergonic (require input of energy to take place), resulting in energy-storing products

What do catabolic reactions do?

Break down large molecules into smaller ones

Give two reasons why catabolic reactions take place

To release energy for cellular processes and for the excretion of waste

Give three examples of catabolic reactions

Respiration, deamination of proteins to release urea, breakdown of macromolecules into monomers during digestion

What reactions do catabolic reactions often include?

Hydrolysis reactions

Are catabolic reactions endergonic or exergonic?

Exergonic (releasing free energy for cellular processes or as excess heat)

What is the modified model of enzyme activity known as?

Induced-fit hypothesis

Explain the induced-fit hypothesis

The enzyme and its active site can change shape slightly as the substrate molecule enters the enzyme, known as conformational changes, ensuring an ideal binding arrangement to maximise the ability of the enzyme to catalyse the reaction.

Give three ways an enzyme can be immobilised

Attachment to an inert substance (eg glass), entrapment within a matrix (eg alginate gel), entrapment within a partially permeable membrane

Give five benefits of immobilising enzymes

No enzyme in the product (uncontaminated) so no further processing to remove it is needed. The enzyme can be reused without later separation. Greater tolerance of temperature and pH changes as they are more stable. Substrates can be exposed to higher enzyme concentrations than in solution. Conditions can be controlled carefully.

Explain how denaturation of enzymes happens

When exposed to high temperatures or extremes of pH, the bonds holding the molecule in its shape start to break, causing the shape of the protein to change, changing the shape of the active site, preventing the substrate from bonding.

Give an overview of photosynthesis

Carbon dioxide is converted to glucose (using hydrogen released by splitting a water molecule) releasing oxygen as a waste product

Give three types of organisms which carry out photosynthesis

Plants, algae, cyanobacteria

Explain how light energy leads to photosynthesis

Within the chlorophyll, light energy results in the excitation of electrons, triggering transfer of electrons, leading to a series of reactions which makeup photosynthesis in which light energy is transformed to chemical energy

Which two regions of the light spectrum do chlorophylls absorb wavelengths from?

Blue-violet and red

Which region of the light spectrum do carotenoids absorb wavelengths from?

Blue-violet

Which end of the visible light spectrum has the longest wavelength?

Red

Give two carbon dioxide enrichment experiments

Enclosed greenhouse experiments and free air carbon dioxide enrichment experiments

Why are carbon dioxide enrichment experiments important?

Establish the effect of carbon dioxide on plant growth and photosynthesis to develop a clearer idea of potential future risks

How do FACE experiments work?

Carbon dioxide is pumped into a natural ecosystem to increase localised carbon dioxide concentrations.

Give one benefit and one drawback of FACE compared to greenhouse experiments

Larger plants and trees can be studied, but other variables cannot be controlled (can be monitored though)

Define a habitat

The place where an organism lives

Give two ways in which a habitat can be described

Geographical location and type of ecosystem

Give eight abiotic factors

Light intensity, temperature, water turbidity, humidity, soil/water pH, soil/water salinity, soil composition, oxygen/carbon dioxide concentration

Give two species as examples for adaptions to abiotic factors

Marram grass and mangrove trees

What abiotic factors are in the habitat where is marram grass found?

Low water availability, high salinity, low nutrient levels

Give four adaptations of marram grass

Adaptations to reduce steep concentration gradient by raising humidity in air surrounding leaf to reduce water loss by evaporation: Leaves are rolled up to reduce exposure of surfaces to the wind, trapping water vapour in the rolled leaf. The stomata are in sunken pits to trap water vapour. The inner surface of the leaf is covered in tiny hairs which trap water vapour. Also, marram grass leaves have a thick waxy cuticle on their outer surface to reduce evaporation.

What type of plant is marram grass?

A xerophyte

Give the abiotic factors found in mangrove swamps

High salinity, low fresh water availability, low oxygen availability (bc submerged in water)

Give the adaptations of mangrove trees

Prop roots, providing stability, pneumatophores growing vertically out of water-logged soil specialised for gas exchange, cells don't allow entry of salt and prevent outward movement of water, or excrete excess salt through salt glands

Define a limiting factor

Any biotic or abiotic factor that restricts the growth of organisms

Define distribution

Where a species is found within an ecosystem

Give a method of investigating limiting factors and species distribution

Transect sampling

What is a transect used for?

A transect is used to measure how the abundance of a species changes along an environmental gradient

What are transects?

Lines laid out across a site

Give four types of transects

Continuous line transect (every species touching the tape measure is recorded), interrupted line transect (species touching the line at regular intervals are recorded), continuous belt transect (quadrats are placed end-to-end along the line), interrupted belt transect (quadrats are placed at regular intervals)

How is rainfall measured?

Rain gauge

How is humidity measured?

Hydrometer

How is dissolved oxygen measured?

Electronic oxygen sensor

How is water turbidity measured?

Turbidity meter

How is light intensity measured?

Electronic light meter

How is landscape relief measured?

Contour lines on a map or a GPS

How is site aspect (direction site faces) measured?

Compass

How is slope incline measured?

Clinometer