3. organisms

variation

is the defining feature of life

discontinuous

when variation can be placed into distinct categories

continuous

when there can be a wide range of possibilites, like a range.

morphological classification

classification system based off of the physical features of organisms created by linnaeus

biological species concept

in order to be classified as the same species, individuals must be able to breed together and produce a fertile offspring.

speciation

the process by which a population is separated into two groups that can no longer reproduce together. one part of the population evolves on way due to certain selection pressures while the other evolves another way.

chromosome number

human: 46

chimpanzees: 48

diploid cells usually have an even umber of chromosomes.

karyogram

representation of the chromosomes found in a cell arranged according to a standard format

chromosome length, shape and centromere position

karyotype

specific number and appearance of chromosomes in their cells.

hypothesis of the evolution of human chromosome 2

going from 48 to 46 there have been various hypotheses

it is hypothesized that the chimpanzees chromosome 12 and 13 fused to form our human chromosome 2.

evidence: shape banding pattern, presence of telomeres in the centre of the human chromosome 2.

genome size to complexity

while genome size may be able to link to complexity in a way it is not a clear indicator. While yeast may not be as complex as we think, it can survive and do things that humans cant, therefore it needs different genes.

phylogenetics

technique for whole genome sequencing, where whole genome sequences of organisms are compared to understand how closely related they are.

personalized medicine

the use of whole genome sequencing to best adapt the prescription given to that persons DNA profile.

difficulties with the biological species concept

does not take into account organisms which reproduce asexually:

using binary fission rather than breeding

or horizontal gene transfer where DNA sequences can be exchanged between bacteria through attachment.

why are hybrids often infertile

because often they are the result of chromosome numbers which sum to an odd number. This atypical chromosome number results in the difficulty of homologous pairs of chromosomes to match up during meiosis, therefore the production of gametes will be difficult.

DNA barcoding

a short sequence of DNA inside an organisms cell that can be used quickly identify the species.

bioindicator/indicator species

organisms which are really sensitive to certain types of pollution that their presence in an ecosystem indicates the lack of pollution.

eDNA

environmental DNA which is collected from an environment rather than an organism is used to give s informaion about that respective ecosystem.

hierarchy of classification

kingdom

phylum

class

order

genus

species

primitive traits

characteristics which have similar structure and function and evolved early in history

derived traits

characteristics which have similar structure and function but have evolved more recently

cladistics

natural system of classification for grouping Taxa based on characteristics that have evolved most recently.

Done through analysing gene or amino acid sequences.

the evolutionary clock

the mutation rate in amino acid sequences can be seen as a type of clock, the more mutations, the further back in time the common ancestor was and the less mutations the more recent.

cladogram parts

node: where a speciation occurs

root: the base from which other species branch out shows the common ancestor

terminal branch: end of a branch which represents the most recently evolved of the organisms in the clade

domains

all living organisms are seperated into tree domains, archea, eubacteria, eukarya

archea

single celled organisms that are distinct from bacteria, very ancient. were first discovered in extreme environments.

Why is it bad that the surface area to volume ratio getting smaller as organisms increase size

• the volume is a reflection of its metabolic need to exchange respiratory gases

• an organisms ability to take in and release substances is limited by its outer layer surface area.

what are gas exchange surfaces characterised by?

• being thin (like only one cell layer) to keep diffusion distances short

• being moist to encourage gas exchange

• having a large surface area, for maximum diffusion

• being permeable to respiratory gases.

why are concentration gradients important?

they must be maintained in order for oxygen to diffuse into the blood and CO2 out of the blood.

Fish gills example

the concentration of respiratory water in the environmental water does not change as long as the body of water maintains good ecological health

When does concentration of O2 and CO2 change within the blood of an organism (1)

• when the blood is first transported to the gills, it has recently been within capillaries of the muscles and other body tissues

When does concentration of O2 and CO2 change within the blood of an organism (2)

• The blood that leaves body tissues contains a higher CO2 concentration and lower O2 concentrations compared to levels before the blood reached the active body tissues.

When does concentration of O2 and CO2 change within the blood of an organism (3)

the blood will then be transported to the gill tissue and exchanges will occur.

what must occur for gills to maintain the concentration gradient?

water must continuously pass over the gills/air myst be continuously refreshed in the lungs

gas diffusion within lungs

• within lungs there are numerous dense capillaries that contain blood that has recently come from respiring body tissues.

• the concentration of O2 in teh lung capillaries in lower than that of air inspired into the lungs

how. is the concentration gradient kept in place

there must be continuous blood flow to the dense network of blood vessels in both the body tissues.

how to lungs maximise their air capacity

by subdividing their volume into microscopic spheres called alveoli

alveolus

each alveolus is at a terminal end of one of the branches of tubes that started as trachea.

surfactant

the inner surface of each alveolus is lined by a thin phospholipid and protein film.

some alveolar cells secrete surfactant which lines the inside of the alveoli, reducing surface tension and preventing collapse during exhalation.

bronchioles

the inside of each lung is subdivided into several lobes, which contain smaller branches called bronchioles that lead to the alveoli.

all the bronchioles are connected to the trachea for access to inspired and expired air.

surface area of lungs

the spherical shape of the alveoli provides a large surface area of diffusion of CO2 and O2

role of the diaphragm

during inspiration, the diaphragm contracts, increasing the volume of the thoracic cavity

role of the external intercostal muscles and abdominal muscles

• during inspiration, these muscles contract to help raise the ribcage which further increases volume in the thoracic cavity.

spirometer

device used to measure lung volume

tidal volume

the volume of air breathed in or out during a typical cycle when a person is at rest

inspiratory reserve volume

the maximum volume of air that a person can breathe in (max point of tidal volume)

expiratory reserve volume

maximum volume of air a person can breathe out (min point of tidal volume)

vital capacity

inspiratory reserve volume+tidal volume+expiratory reserve volume.

A leaf…

has many adaptations to help facilitate this exchange of gases

A waxy cuticle

• a wax lipid layer that covers the surface of the leaves, prevents uncontrolled and excessive water loss by evaporation.

An upper epidermis

small cells on the upper surface of leaves that secrete a waxy cuticle.

spongy mesophyll

loosely packed cells are located under the palisade layer and just above the stomata

have a few chloroplasts and many air pocket spaces, providing large surface area for gas exchange.

veins

• structures which enclose the fluid transport tubes (xylem+phloem)

• veins are locacted centrally within a leaf, to provide access to all the cell layers

Stomata

numerous microscopic openings on the lower surface of leaves. each stoma is composed of 2 guard cells

• a pair of guard cells create an opening and closing

what occurs when the stomata are open

permit CO2 to enter the leaf and at the same time water vapour and oxygen to exit the leaf

transpiration

the evaporation of water through open stomata

factors affecting rate of transpiration (increased light)

rate increases

• light stimulates guard cells to openn

• increased light stimulates photosynthesis

• open stomata permit diffusion of CO2 and O2

factors affecting rate of transpiration (increased temperature)

increases

• increased molecular movement including evaporation of water

factors affecting rate of transpiration (increased wind speed)

increases

wind removes water vapour at the entrance of teh stomata

factors affecting rate of transpiration (increased humidity)

decreased

increased humidity lessens the water concentration gradient between the in and out of the leaf

structure of haemoglobin

• 4 polypeptides and has quaternary structure.

• each polypeptide has a haem group near the centre with iron within them

haemoglobin binding

• when haemoglobin reversibly binds to an O2 molecule, its the iron thats actually bonding with it.

• haemoglobin has a total of 4 iron atoms so it has a capacity to hold 4 O2 molecules

saturated haemoglobin

when bonded to 4 O2 atoms

Cooperative binding oxygen to haemoglobin

any oxygen molecule bonded to haemoglobin increases its affinity for oxygen

which haemoglobin form has the greatest affinity

haemoglobin with 3 oxygen molecules

why?

each molecule of oxygen bonded to haemoglobin changes its shape in a way that increases its affinity.

allosteric binding of CO2 to haemoglobin

the binding of CO2 to the polypeptide chains of haemoglobin and the resulting change in haemoglobin affinity for oxygen.

Foetal haemoglobin

in the placenta…

the capillaries of the mother are very close to those of the foetus

this allows molecular exchanges to occur with CO2 and O2

the mother is breathing, foetus is not

the foetus is actively carrying out cell respiration, the blood sent to the foetal side is low in O2 and high in CO2

this concentration gradient encourages the diffusion of the mother oxygen to the foetus

what happens when haemoglobin bonds to CO2 (BOHR SHIFT)

its affinity for oxygen decreases

haemoglobin has a greater tendency to give up oxygen molecules in the presence of CO2