phys 214. planets and life - queen's u

Phys 214. Planets and Life

Dr. Cristina Buzea

Department of Physics

Room 259

E-mail: [email protected]

(Please use PHYS214 in e-mail subject)

Lecture 12. The nature of life on Earth. Evolution.

Defining life. Cells

February 1st

ContentsContents

• Textbook pages 148-164

• What is life?

• Evolutionary adaptation

• The mechanism of evolution

• Natural selection

• Cells - basic units of life

• Earth - Carbon based life

• Silicon based life

• Molecular components of cells

Movie (13 minutes) Award winning series - Cosmos. Carl Sagan.

(Not found online)

What is life?What is life?

1. Order

2. Reproduction

3. Grows and develops

4. Energy

5. Responds to the environment

6. Evolutionary adaptation

Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Molecules in living organisms exhibit order.

They are arranged in patterns that make cell

structures.

Exception: crystals.

Spiral patterns in two single celled organism

The presence of order in living organisms is a necessary

condition, but not a sufficient condition for life


1. Order

2. Reproduction


4. Energy




Living organisms reproduce or are products of

reproduction. All organisms have finite lifetimes

and eventually die. Reproduction corrects for this.

A single-celled organism (amoeba) dividing into two cells.

Exceptions:

Mule - is sterile and cannot reproduce even though it is the

product of reproduction between a horse and a donkey

Viruses - incapable or reproducing on their own, need a

living organism.

Prions - infectious proteins, mad cow disease.

The type of reproduction that occurs between human

beings is referred to as sexual. Bacteria reproduce by

the process of cell division (asexual).


1. Order

2. Reproduction


4. Energy




Living organisms grow and develop in patterns

in part by heredity, traits passed to an organism

from its parents.

Nile crocodile emerging from its shell.

Exception:

fire


1. Order

2. Reproduction


4. Energy




Energy utilization in living organisms is

one of the most basic requirements of life,

without which organisms could not maintain

order, grow, and reproduce.

Tube worms living near deep-sea vents obtain energy from

chemical reactions made possible in part by heat released

from the volcanic vent.

Exceptions: Some organisms can survive for

very long period of times in dormant state.


1. Order

2. Reproduction


4. Energy




Life interacts with the surroundings and

responds to environmental changes.

A jackrabbit’s ears flush with blood, the blood flow adjusts

automatically to help the animal maintain a constant

temperature by adjusting the heat loss from the ears.

Exceptions: human-made devices

(thermostat)


1. Order

2. Reproduction


4. Energy




Life evolves as a result of the interactions

between organisms and the environment,

leading over time to evolutionary

adaptations that make species better suited

for the environment.

A pygmy seahorse is camouflaged in its coral surroundings.

When the adaptations are significant, these organisms

may be very different from their ancestors – that they

constitute a new species.

Evolutionary adaptation

Species = groups of organisms that are genetically distinct.

• the precise border between the two species is not always clear (especiallymicro-organisms)

Once a species is identified is given a name consisting of two parts:

italics

Homo sapiens

Horses and donkeys

Equus caballus and Equus asinus

Species

(specific)

Genus

(generic)

Evolutionary adaptation

Of the six basic properties of life, biologists consider the most fundamental to

be evolutionary adaptation.

Evolution - ancient idea

Anaximander (c. 610-547 B.C.) – life arose in water and evolved to more

complex forms

Empedocles (c. 429-432 B.C.) – creatures poorly adapted perish

Jean Baptiste Lamark – early 1800 – relationship between fossils and living

organisms = life forms evolved by gradually adapting to perform

successfully in their environments; not able to explain how evolution

worked

Charles Darwin – “The origin of species” 1859

The mechanism of evolution

Charles Darwin – “The origin of species” 1859

Fact 1: Overproduction and competition for survival

population has the potential to produce more offspring than the

environment can support (food, shelter) = > competition for

survival

Fact 2. Individual variations: individuals vary in many heritable

traits; some traits make them better to compete for survival

Conclusion: unequal reproductive success = natural selection

Individuals whose traits best enable them to survive and reproduce

will, on average, leave the largest number of offspring that in

turn survive to reproduce.

Evidence for evolution by natural selection

The different species of finches found on the Galapagos islands are evidence ofDarwin’s theory of natural selection because they have all evolved adaptationsfrom a common ancestor to suit the environmental conditions found ondifferent islands.

Darwin backed up his claim by

documenting cases of related

organisms adapted to different

environments or lifestyle.

Evidence for evolution by natural selection

Darwin discovered fossils ofextinct organisms clearlyrelated to modern organisms(giant armadillos).

Darwin realized that naturalselection explains differencesnot only between closelyrelated modern species(finches), but larger changescan occur over a long time ->extinction of some speciesand appearance of others.

Artificial selection – selective breeding of

domesticated plants and animals by humans

over the few thousands of years.

Dogs breeds with common ancestors –

Rottweilers and Chihuahuas

Evolution by natural selection

Evolutionary adaptations are related to changes that occur through time in

DNA

The most basic definition of life which takes account of the relative

importance of the six fundamental properties of living things is that life is

something that can reproduce and evolve through natural selection.

Evolution by natural selection

Movie (13 minutes)

Award winning series - Cosmos.

Carl Sagan.

Disk 2. Ch. 1-4. [0:00 – 13:00]

Natural selection, artificial selection.

Cells - the basic units of life

The basic biological structures of life on Earth are called cells.

• Some organisms consist of single cells, others are complex structures with trillions ofcells working cooperatively, having specialized tasks.

• Life elsewhere might be composed of cells, might not have the same biochemistry asEarth cells.

The fact that all cells used in life on Earth are based on the same biochemistry suggests thatall life on Earth shares a common ancestor.

only left-handed amino acids; the same molecule - ATP - to store and release energy; passeshereditary information in the same way with DNA.

Earth life is carbon based

• Life on Earth made of more than 20

elements

• More than 96% of the mass of living

cells are made of carbon, hydrogen,

oxygen, and nitrogen

• The molecule that accounts for cell

structure and function - Carbon

Earth life is carbon based

• Carbon - ideal as a fundamentalbuilding block of biologicalmolecules

• It readily forms chemical bonds withitself and other elements, allowing awide variety of complex molecules toform!

• 4 = Maximum number of atoms thatcarbon can bond

• Single and double bonds

Chemists refer to molecules containingcarbon atoms as organic.

Complex organic molecule. One bond links Cto an amino group (green)

Silicon based life?

Is silicon an obvious alternative to carbon as a building block for

biological molecules?

It has a similar electronic structure to carbon, forming a maximum

of four bonds and, hence, but does it have a similar chemistry?

Silicon forms its strongest chemical bonds with oxygen.

Silicon based life - unlikely!

Reason why silicon is unsuitable as a building block for life compared to carbon

1. Silicon–silicon bonds are much weaker than carbon–carbon bonds

2. Silicon does not form multiple bonds with itself, limiting the complexity ofmolecules it can form

3. SiO2 is a high melting point solid and, hence, cannot be used to transfer siliconatoms like gaseous CO2 can be used to transport carbon atoms!!

Silicon ~ 1000 times more abundant in Earth crust than carbon

Life on Earth is based on carbon

Carbon (organic) molecules found in space - meteorites, interstellar dust, Joviansatellites

Why?

Molecular components of cells

Carbohydrates

• MOST important role - short-term energy storage

• Provide energy to cells (sugarsand starches)

• Make important cellularstructures (celulose - fibers ofcotton and linen, mainconstituent of wood)

Lipids

• MOST IMPORTANT - Majoringredient of cell membrane(Membrane forming role -critical in the origin of life -spontaneously form membranesin water)

• Long term energy storage(known as fats)

Nucleic acids

Most important - the storage and transfer of

information

DNA - The basic hereditary material on Earth

RNA (ribonucleuc acid) - helps carry out instructions

contained in DNA

More on DNA later

Proteins

• basic functioning of living organisms

• Vast array of functions

• Structural elements

• Enzymes - important to almost all biochemicalreactions, including copying genetic material,serving as catalysts

• Most important - enzymes - facilitate replicationof DNA and the reading of the genetic code

Amino acids

The basic molecular building blocks of proteins are amino acids.

• Amino refers to the amino group (one nitrogen and 2 hydrogen); also contain a carboxyl group(CCOH).

• Different amino acids - distinguished by different sets of atoms bonded to the central carbon

More than 70 amino acids identified, but life on Earth uses only 20! => all life on Earthhas a common ancestor.

Amino acids found in protein in life on Earth are all left-handed molecules.

Next lecture

• February 4th. Midterm exam review

Common mistakes

Calculations

Marking of calculations

I encourage you to solve the quantitative problems from the textbook!

February 6th - Midterm exam!

1 hour, multiple choice questions + images description + calculations

phys 214. planets and life - queen's u

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