Biology Unit 6 Explanation & Notes

Section 12.1 – The Fossil Record – how old is it?

There are several ways fossils can form:

Permineralization – minerals carried by water surround the hard structure, may even replace it

Natural casts – flowing water removes bone and tissue and then minerals fill in mold recreating original shape of organism

Trace fossils – Signs of organism activity such as nests, footprints, and imprints of leaves

Amber-preserved fossils – tree resin (sap) traps organisms and then hardens into amber

Preserved remains – entire organism is encased in ice, volcanic ash, or bog (dead plant material)

Erosion and earthquakes can uncover fossils millions of years later. How do scientists know how old it is? Here are two terms that involve “dating” fossils:

Relative dating – show when a fossil lived by comparing its location in the layers of rock with other fossils (just gives an idea of when it lived, not accurate in telling how old)

Radiometric dating – calculates the natural decay rate of unstable isotopes found in materials to find the age (more precise)

An isotope has the same number of protons but different number of neutrons. The half-life of an isotope is the amount of time for half of it to decay into a different element. This is how scientists can measure how old something is.

Section 12.2 – The Geologic Time Scale – organizing earth’s history

Since the earth is 4.5 billion years old, it has gone through various geological changes so scientists have categorized them into measurable units.

An index fossil shows when an organism had existed during a certain span of time over a large area; useful for estimating age of rock layers. Using such evidence, scientists came up with the geologic time scale which represents the history of earth by major events or changes. An epoch is the smallest unit of geologic time that lasts several million years. A period is a common unit of time that lasts tens of millions of years and is associated with a type of rock system. The largest is an era which lasts tens to hundreds of millions of years and has two or more eras. **partner up! Complete #5 on pg. 4 and all of pg. 5 in your unit 6 SAW

Section 12.3 – The Origins of Life – how’d it begin?

Regarding how life began, most scientists agree on two key points: (1) Earth is billions of years old, and (2) the conditions and atmosphere are very different from today. The most commonly accept hypothesis is that Earth formed from over millions of years of colliding debris of gas and dust that orbited the sun (made from a nebula – condensed clouds of gas and dust). Eventually Earth cooled down, continents formed, and water began to collect which allowed organic molecules to develop. Here is where scientists are not exactly sure how life forms!

There are two organic molecule hypotheses. One is derived from the Miller-Urey experiment which simulates lightning turning gases and water into organic compounds; suggesting that electrical energy sparked the creation of life. The other is the meteorite hypothesis which suggests that organic molecules found in meteorites (landed on earth) may have been present when Earth formed or later with meteorite and asteroid impacts.

One hypothesis suggests that RNA was the first storage of genetic material rather than DNA in early life. Ribozymes are molecules that catalyze reactions leading to replication of RNA without the help of enzymes (unlike DNA). Short RNA chains may have formed membranes to protect chemical reactions leading to complex organic material and eventually simple life!

How do you think life formed on Earth?

Section 12.4 – Early Single-Celled Organisms – microbes to eukaryotic cells

The earliest form of life based on fossil records (3.5 billion years ago) was photosynthetic. Cyanobacteria are bacteria (earliest forms of life) that can carry out photosynthesis and deposited minerals as well as release oxygen which allowed the evolution of aerobic prokaryotes.

Around 1.5 billion years ago, eukaryotes (complex cells) may have formed from endosymbiosis which is a relationship in which one organism lives within the body of another and both benefit from the relationship. This explains how chloroplasts and mitochondria have developed inside cells. Over time, you would get complex and multi-cellular organisms. Eventually, asexual reproduction leads to sexual reproduction which increases genetic diversity and life on Earth.

**skip pages 21-22

Section 12.5 – Radiation of Multicellular Life – from ocean to land

Multicellular life appeared during the Paleozoic (“ancient life”) era about 544 M.Y.A. (million years ago). The Cambrian explosion is the earliest part of the Paleozoic era where a huge diversity of animal species evolved; especially marine invertebrates into land vertebrates like amphibians. A lot of coal comes from fossils from this era (your car runs on dead animals!)

The Mesozoic (“middle life”) era was about 248 M.Y.A. and is known as the Age of Reptiles. Dinosaurs, flowering plants, birds, and sharks all evolved. Ended with a mass extinction by a massive meteorite sending dust and debris in the atmosphere prevent sunlight and ultimately causing the dinosaurs extinction.

The Cenozoic (“recent life”) era began about 65 M.Y.A. and is known as the Age of Mammals. Egg-laying and placental mammals evolved and diversified. The earliest ancestors of modern humans, primates, also evolved. Homo sapiens (modern humans) have been around for about 100,000 years. Question: What percent of time is that compared to the age of earth?

Section 12.6 – Primate Evolution – who are our ancestors?

Primates are mammals with flexible hands and feet, forward-looking eyes (3D vision) and large brains relative to body size. Lemurs, monkeys, apes, and humans all have similar physical traits.

One of the main subgroups of primates, and the oldest, is prosimians which are small, active at night just like lemurs. Anthropoids include monkeys and hominoids, which can be broken down into great apes and hominids. Hominids walk upright, long lower limbs, opposable thumbs and large brains. Why do you think it is important to be bipedal (walk on two legs)? Could humans have evolved without walking on two feet?

**partner up! complete pg 30-31 in your unit 6 SAW!

Section 18.1 – Studying Viruses and Prokaryotes – what causes infections?

A virus is an infectious particle made only of a strand of DNA or RNA with a protein coat. Bacteria, however, are one-celled organisms that can also cause infection. Any organism or particle that can cause an infectious disease is called a pathogen. Another example is a viroid which is an infectious particle that causes disease in plants. They have a single-strand of RNA without a protein coat.

On the border of life and nonlife is the prion. A prion is an infectious particle made only of proteins that causes other proteins to fold incorrectly. They have no genetic material and the body has no immune response to proteins (cause of mad cow and other brain diseases).

Section 18.2 – Viral Structure and Reproduction – how they infect and spread!

Viruses have a basic structure in which their genetic material is surrounded by a protein shell called a capsid. They can only reproduce after infecting a host cell; they have no organelles that need oxygen or ATP. The shape and structure of the virus allows them to “lock” onto protein receptors of a host cell and includes three basic shapes: enveloped (spherical with spikes), helical (long, coiled shape), and polyhedral (many-sided). Viruses can only have either DNA or RNA; never both!

One group of viruses is those that attack bacteria called bacteriophages. When attached, the bacteriophage injects the host cell with its DNA, like a syringe.

There are two types of infections caused by viruses: lytic and lysogenic. A lytic infection is where the host cell bursts, releasing new viral offspring into the host’s system. A lysogenic infection is where the phage combines its DNA into the host cell’s DNA. For lytic, think of pirates taking over a ship, robbing it’s treasure, capturing its sailors, and then burning it down. For lysogenic, think of getting bit by a vampire and then you’re hunting humans to bite as well!

Section 18.3 – Viral Diseases – infectious diseases and vaccines

Question: is a cold caused by cold weather? By spending more time indoors you increase the chance of getting sick due to contact. So, wash your hands!

Your skin is the first defense against a virus. They will have to enter through a cut in the skin or through a mucous membrane or body opening. The next line of defense is your cells receptors that guard against intruders but a virus can “unlock” those receptors and trick a cell into allowing it in. *HIV CASES 2008

Example of human illnesses caused by viruses:

Common cold – 200 known viruses that causes a cold; always mutating which makes it hard to cure

Influenza – “flu” virus that can spread quickly in an epidemic which is a rapid infectious outbreak affecting many people (20% of people in the U.S. every year by the flu).

HIV – a retrovirus, a virus that contain RNA and uses an enzyme to make DNA, that can remain dormant for years in a lysogenic infection and then attacks the white blood cells as a lytic infection which causes AIDS, acquired immune deficiency syndrome.

A vaccine, substance derived from a weakened viral strained, helps the immune system respond against microbe invasion and protects against future invasions before they cause harm. **Complete p.51 in your unit 6 SAW (you’ll need your textbook pg. 554).

Vocabulary Buster! – Relevant terms from section 18.4, 18.5, and 18.6

Section 18.4 – Bacteria and Archaea **skip pg. 61-62

Obligate anaerobe – prokaryotes that cannot live in the presence of oxygen; oxygen poisons them. Example is archaea that makes methane gas in bottom of lakes and digestive tracts of cows and sheep.

Obligate aerobe – prokaryotes that need the presence of oxygen. Examples are pathogens that cause tuberculosis and leprosy.

Facultative aerobe – prokaryotes that can survive with or without oxygen

Plasmid – small piece of genetic material that can replicate separately from the prokaryote’s main chromosome

Flagellum – long, whip-like structure outside the cell that helps it move

Conjugation – prokaryotes exchanging parts of their chromosomes through a bridge

Endospore – a cell with a thick, protective wall that can survive harsh conditions and disinfectants

Section 18.5 – Beneficial Roles of Prokaryotes

Bioremediation – a process that uses microbes and other living things to break down pollutants; can be used to clean up oil or chemical spills

Section 18.6 – Bacterial Diseases and Antibiotics

Toxin – a poison that is released by an organism; bacteria can produce toxins that travel through the bloodstream

Antibiotics – chemicals that kill or slow bacteria growth; works by preventing bacteria from making cell walls

Antibiotics can be overused causing natural selection of harmful bacteria that are resistant. If underused, only the weaker bacteria would be killed while the strongest would survive and become drug resistant. Also, antibiotics can be misused on livestock to increase their rate of growth which in turn creates drug-resistant pathogens in them.

Class lab Activity! – turn to pg. 74-75 to complete the virtual lab together as a class