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Which of the following make C. elegans an ideal species to study interms of understanding the human body?

A. Its sexual reproduction requires a male and a female.
B. Its genotype is very simple, which means that it is a simpleorganism.
C. It has a long time of gestation, which allows a detailed view ofits development.
D. It has a long lifespan, which allows for important longitudinalstudies.
E. The number of cells in the animal does not increase, the cellsonly grow larger.

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Related questions

Andrea Smith was taking notes for her biology exam. Her professor has told her that the exam would cover, in part, the di erences between sexual and asexual reproduction. As she reviewed her notes and prepared for today’s class, she was thinking about her own reproductive dilemma. If only asexual reproduction were the case for humans, maybe she wouldn’t be in this mess. Or at least there wouldn’t be questions about who was the father of her twins. “Dwelling on it isn’t going to help me prepare for class, and right now I have got to nish this chapter on animal reproduction,” she thought. She tried to concentrate and forget about her current dilemma as she feverishly typed on her notepad:

Asexual or sexual reproduction: 3 types of asexual reproduction: (1) ssion: separation of a parent organism into two or more individuals of equal size, (2) budding: growth of new individuals from outgrowths of existing organisms, and (3) fragmentation accompanied by regeneration: the breaking of the body into several pieces, some or all of which develop into new complete individuals through the regrowth of lost body parts. NOTE: Be able to explain the di erences between sexual and asexual reproduction!

She suddenly let out a long sigh. “It’ll be ne,” she thought. “I just hope that none of my family or friends watches the show. What was I thinking when I agreed to this? But that’s what Xavier wanted, and I will do whatever it takes to prove he is the father. Besides I am going to need the money if I have to take care of these babies on my own!”

e next day in class she was feeling even more nervous and was becoming increasingly angry as she thought about her current situation. Her thoughts were interrupted by the sound of her professor’s voice:

“OK, class,” her teacher was saying, “that wraps up asexual reproduction. Let’s move on to reproductive cycles
and patterns. Most animals exhibit cycles in their reproductive activity. Reproductive cycles are often controlled
by hormonal and environmental cues. Animals may reproduce either exclusively asexually or sexually while other animals alternate between the two methods. For example, some animals can lay eggs of two types, depending on
the environment and/or season. One egg type matures only if it is fertilized while the other type does not require fertilization for development, a process called parthenogenesis. Some animals, and in rare cases humans, have both male and female reproductive systems. Some hermaphrodites can fertilize themselves, but most must mate with a member of the same species. Please look over these handouts and answer the questions that follow.”

As the other students read through the assignment, Andrea was thinking: “I’m dealing with a case of sexual reproduction that no doubt started with the fertilization of my egg with, hopefully, Xavier’s sperm. at reminds me, I need to make sure I go over internal and external fertilization again in my notes. I’m not sure I completely understand it.”

All this started the night Xavier had come came over to talk to Andrea about their break-up. He had smelled and looked so good that evening. e events of that night had left Andrea wondering if there was really some truth to that stu about pheromones, which Andrea has learned in her class were chemical signals released by one organism that in uence the behavior of another individual of the same species. Even though Andrea had met someone else and had

“An Unusual Case of Animal Reproduction” by Powell and Tillman Page 1

been seeing Neo for a while, she hadn’t been able to resist Xavier. Neither she nor Xavier had behaved like themselves that night. It was unlike them not to use some barrier method of contraception. As the class wrapped up, Andrea’s mind was still on her upcoming appearance on a daytime talk show. In some ways she was dreading it; but she was determined to prove what she believed she had known all along: at Xavier was the father of her twins.

Questions

1. What is the di erence between asexual and sexual reproduction?
2. List and de ne some types of asexual reproduction. Give one example of each. 3. What is the di erence between parthenogenesis and hermaphroditism?
4. What is the di erence between internal and external fertilization?
5. What is the function of pheromones?

NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE

“An Unusual Case of Animal Reproduction” by Powell and Tillman

Page 2

Part II – The Pregnancy

“I can’t believe it has come to this! Airing our dirty laundry on national television. I never thought Xavier would let things get so out of hand.”

It was late and Andrea was so upset she couldn’t sleep. She tried studying for the upcoming exam, but she couldn’t concentrate. She decided to get an early start on packing. She was so angry with Xavier. How could he have left her pregnant and alone, she thought, as she neatly added her new dress to the bag? How could he think that their babies might belong to someone else? She grabbed her journal, about to add it to the bag, but instead sat in her cozy corner chair and began to read:

January 12, 2007

I’m pregnant with twins! Sometimes it’s still hard to believe because it was so unexpected. I feel like I am about to pop! I know that Xavier is the father of my babies and I can’t wait for us to be a family. But he has doubts about it all because he knows that I met someone else during the brief time that we split up. And he wants to be sure that he is the father before we can move on. But what if it is Neo, the new guy I met? ere’s a slight chance but I doubt it. I know the exact time of conception. It was the night Xavier came over to talk about our relationship. It was a little over a week after that night that the pregnancy test detected the increase in HCG. I guess I just missed him so much.

I do regret that Xavier hasn’t been around much during the pregnancy. He has missed the development of our babies. In the past months, I have heard the babies’ heartbeats and felt them moving around. I wish he would come back because it’s obvious that I am pregnant now. Hopefully we can talk through our di erences and get back together before the pregnancy gets di cult—the frequent urination and back pain my OB/GYN keeps warning me about. I know there is no way he will ever let me go through labor alone. I only pray the contractions are not more than I can bear. Xavier seems committed to the idea of a paternity test. Hopefully it won’t come to that, but if it does, we’re going to a daytime show to gure all this out.”

“Wow! at seems like a lifetime ago,” she thought. “Now we have these beautiful twins and we don’t seem any closer to becoming the real family I dreamed about. Well this will all be over in a couple of days. I am 110% con dent that the twins belong to Xavier, not Neo. I can’t wait to see the look on Xavier’s face and hear him apologize once he sees the results of the paternity test!”

Questions

1. What does Andrea mean by time of conception?
2. How is HCG used to determine pregnancy?
3. List some changes that occur with the fetus/mother during the 1st, 2nd, and 3rd trimesters. 4. What hormones are responsible for inducing and regulating labor?
5. What trimester is Andrea in during this journal entry?

NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE

“An Unusual Case of Animal Reproduction” by Powell and Tillman

Page 3

Part III – The Results

Andrea replayed the words over and over again in her mind: “Xavier, you ARE the father!” She was ecstatic. Finally, she could breathe, knowing that Xavier was the father of her babies. en she heard what the host had to say next...

“Neo...YOU ARE the father!”
Andrea looked around in disbelief. She heard herself saying, “What do you mean? You just said Xavier was the father!

If Xavier is the father, how can he be the father?” she asked as she pointed toward Neo.

“Well, this is a rst, even for our show. But it appears that your twins were fathered by both of these men.”

“I can’t believe it. e rst time I do something like this and I end up with twins and two fathers! Not only did I expose myself to potentially deadly STDs, but now I have two children, whom I have no doubt that I will be raising alone, and I have put my school career in jeopardy,” Andrea thought.

She still couldn’t believe this was really happening to her. How was it possible that her TWINS have di erent fathers? What were the events that must have happened within her body that could lead to these circumstances? She grabbed her

journal from her bag and ipped back to the entry describing her feelings the day she found out she was having twins:

August 23, 2006

I just came back from another Dr’s appointment. Dr. Blossom informed me that I am having two babies— twins—fraternal. I don’t know if they are boys or girls yet. One could be a boy and the other a girl. I still can’t believe this has happened. Xavier has to be the father. He has to be! I will have to just play the hand I have dealt myself. How stupid was I? I was going to practice abstinence after Xavier and I broke up...and I certainly wasn’t planning on meeting and getting involved with Neo! I can’t believe that Neo and I didn’t use a condom either. And it’s no excuse that we had been drinking. I just got caught up in the moment with Xavier—going down memory lane and things got all sentimental. I could have at least thought to use the rhythm method and kept track of when ovulation may occur. is has to be the most irresponsible thing I have ever done! Why did I stop taking my birth control pills anyway? And I have no idea where I put that diaphragm. Undoubtedly, some people will judge me as the type of woman who should have a tubal ligation that would permanently prevent any pregnancy.

Everything hit her at that very second. She closed her journal and just sat there for a moment. Andrea was reminded that she had stopped taking the pill the month before she became pregnant. She remembered that physicians recommend that a woman wait at least one cycle after she stops taking the pill before becoming pregnant because there is a chance that multiple ovulations may occur. Did it have something to with oogenesis? Andrea was so confused she just couldn’t keep things straight in her mind. She thought about it for a minute to let it all sink in.

Andrea sat back and thought about the lecture on animal reproduction the week before. She pulled out her lecture notes on the menstrual cycle, the basic foundation of everything that she was going through.

Questions

1. Describe the two types of cycles that occur in female mammals (menstrual vs. estrous).

2. Compare and contrast the sterilization techniques (vasectomy and tubal ligation) and the temporary and reversible methods discussed in the case.

3. What are the functions of GnRH, FSH, LH, estrogen, and progesterone?

4. How can the paternity results be explained? Your answer should consider the amount of time before and after ovulation a woman is at risk for pregnancy and how long sperm can survive in the reproductive tract. Your discussion may include the following terms: ova, oogenesis, and fertilization, etc.

•

Image in title block dervied from licensed image © CLIPAREA.com—Fotolia.com, ID #21458691. Case copyright held by the National Center for Case Study Teaching in Science, University at Bu alo, State University of New York. Originally published December 8, 2011. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE

“An Unusual Case of Animal Reproduction” by Powell and Tillman Page 4

Andrea’s Lecture Notes: The Female Reproductive Cycle

(I) e female reproductive cycle involves both the uterus and the ovaries:

Menstrual cycle = uterine cycle
• Refers to the speci c changes that occur in the uterus

Ovarian cycle
• Cyclic events in the ovaries that regulate the menstrual/uterine cycle

(II) Hypothalamus secretes gonadotrophin-releasing hormone (GnRH) which stimulates the anterior pituitary to secretefollicle stimulating hormone (FSH) and luteinizing hormone (LH) into the blood. FSH and LH regulate the ovarian cycle.

~OVARIAN CYCLE:

Folicular Phase

FSH and LH stimulate a follicle to grow

e growing follicle releases estrogen

Ovulation

• An LH surge triggers ovulation

Luteal Phase

LH stimulates ruptured follicle to become corpus luteum

Corpus luteum secretes estrogen and progesterone, which inhibits LH and FSH secretion from the pituitary

Corpus luteum disintegrates

Estrogen and progesterone levels decrease, releasing the inhibitory e ect on the hypothalamus and the

pituitary

FSH and LH are released and a new cycle begins

(III) Ovarian hormones, estrogen and progesterone, regulate the uterine (menstrual) cycle ~UTERINE CYCLE:

Proliferative Phase

• increasing estrogen levels causes the uterine lining (endometrium) to thicken: prepares the uterus for

implantation of the blastocyst

Secretory Phase
• increased levels of estrogen and progesterone following ovulation maintains the endometrium by increasing

blood supply and growth of endometrial glands that secretes nutrients

Menstrual Flow Phase
• decreased levels of estrogen and progesterone cause the uterine arteries to spasm, depriving the endometrium

of blood: endometrium disintegrates, resulting in menstruation

Based on the information in the case study, Animal Reproduction, please answer the following questions.

Andrea is pregnant and is trying to calculate the time of conception.What is time of conception and how is it determined?

What are the functions of GnRH, FSH LH, estrogen and progesterone in pregnancy?

Andrea is having twins but the babies have two different fathers.Explain the difference between fraternal and identical twins.Which are these?How could the babies have different fathers?

1.

__________ are fairly small organelles that provide a safe place within the cell to carry out certain biochemical reactions that generate harmful, highly reactive oxygen species. These chemicals are both generated and broken down in the same location.

Lysosomes
Endosomes
Peroxisomes

Nucleosomes

2.

Biologists cannot possibly study all living species. Instead, they try to understand cell behavior by studying a select subset of them. Which of the following characteristics are useful in an organism chosen for use as a model in laboratory studies?

rapid rate of reproduction
all of the above
ability to grow under controlled conditions

amenability to genetic manipulation

3.

By definition, prokaryotic cells do not possess __________.

ribosomes.
a nucleus.
membrane bilayers.

replication machinery.

4.

Cell biologists employ targeted fluorescent dyes or modified fluorescent proteins in both standard fluorescence microscopy and confocal microscopy to observe specific details in the cell. Even though fluorescence permits better visualization, the resolving power is essentially the same as that of a standard light microscope because the resolving power of a microscope is limited by the __________ of light.

intensity
absorption
wavelength

filtering

5.

Choose the phrase that best completes this sentence: Microtubules ____________ and are required to pull duplicated chromosomes to opposite poles of dividing cells.

generate contractile forces
can rapidly reorganize
are found in especially large numbers in muscle cells

are intermediate in thickness

6.

Despite the differences between eukaryotic and prokaryotic cells, prokaryotes have proteins that are distantly related to eukaryotic actin filaments and microtubules. What is likely to be the most ancient function of the cytoskeleton?

cell division
cell motility
vesicle transport

membrane support

7.

DNA and RNA are different types of nucleic acid polymer. Which of the following is true of DNA but not true of RNA?

It contains thymine.
It has 5'-to-3' directionality.
It is single-stranded.

It contains uracil.

8.

Double covalent bonds are both shorter and stronger than single covalent bonds, but they also limit the geometry of the molecule because they ____________________.

prevent additional bonds from being formed with the bonded atoms.
limit the rotation of the bonded atoms.
create a new arrangement of electron shells.

change the reactivity of the bonded atoms.

9.

Drosophila melanogaster is a/an __________. This type of animal is the most abundant of all animal species, making it an appropriate choice as an experimental model.

mammal
amphibian
bird

insect

10.

If the isotope 32S has 16 protons and 16 neutrons, how many protons, neutrons, and electrons will the isotope 35S have, respectively?

16, 19, 17
16, 19, 15
16, 19, 16

16, 20, 15

11.

Living systems are incredibly diverse in size, shape, environment, and behavior. It is estimated that there are between 10 million and 100 million different species. Despite this wide variety of organisms, it remains difficult to define what it means to say something is alive. Which of the following can be described as the smallest living unit?

cell
organelle
protein

DNA

12.

Macromolecules in the cell can often interact transiently as a result of noncovalent interactions. These weak interactions also produce stable, highly specific interactions between molecules. Which of the factors below is the most significant in determining whether the interaction will be transient or stable?

the concentration of each molecule
the size of each molecule
surface complementarity between molecules

the rate of synthesis

13.

Many of the mechanisms that cells use for maintenance and reproduction were first studied at the molecular level in bacteria. Which bacterial species had a central role in advancing the field of molecular biology?

E. coli
S. pombe
C. elegans

D. melanogaster

14.

Many types of cells have stores of lipids in their cytoplasm, usually seen as fat droplets. What is the lipid most commonly found in these droplets?

cholesterol
isoprene
triacylglycerol

palmitic acid

15.

Mitochondria contain their own genome, are able to duplicate, and actually divide on a different time line from the rest of the cell. Nevertheless, mitochondria cannot function for long when isolated from the cell because they are __________________.

anaerobes.
viruses.
parasites.

endosymbionts.

16.

Mitochondria perform cellular respiration, a process that uses oxygen, generates carbon dioxide, and produces chemical energy for the cell. Which answer below indicates a correct pairing of material “burned” and the form of energy produced during cellular respiration?

fat, protein
sugar, fat
sugar, ATP
fat, ADP

17.

Polar covalent bonds are formed when the electrons in the bond are not shared equally between the two nuclei. Which one of these molecules contains polar bonds?

propane
methane
molecular oxygen
water

I JUST NEED SIMPLE/BASIC ANSWERS NOT LONG ANSWERS

1. Explain how life can be viewed at different levels of biological complexity.

2. Explain how researchers study biology at different levels, ranging from molecules to ecosystems.

3. Distinguish between discovery-based science and hypothesis testing, and describe the steps of the scientific method.

4. Tell whether a given topic or research study is about biology. Tell whether that study is discovery-based or hypothesis testing, or both.

5. If presented with a research study, propose what the Research Question was.

6. If presented with an example, tell whether a statement is a hypothesis, theory or law and why you think so.

Describe the general structure of atoms and their constituent particles.

Relate atomic structure to the periodic table of the elements. List the elements that make up most of the mass of all living organisms.

Explain how a single element may exist in more than one form, called isotopes, and how certain isotopes have importance in human medicine.

Compare and contrast the types of atomic interactions (bonds) that lead to the formation of molecules.

Tell which atoms and how many of each make up a given molecule (formula or diagram).

For a bond in a given molecule, tell whether the bond is covalent, and if it is, tell whether it is polar or nonpolar and why you think so.

Explain the concept of electronegativity and how it contributes to the formation of polar and nonpolar covalent bonds. Tell whether a given atom is electronegative or not, and why you think so. Label partial charges in a polar bond.

Draw five water molecules and label the atoms and bonds within and between the 5 molecules.

Describe how hydrogen bonding determines many properties of water.

List the properties of water that make it a valuable solvent, and distinguish between hydrophilic and hydrophobic substances.

Explain how water has the ability to ionize into hydroxide ions (OH–) and into hydrogen ions (H+), and how the H+ concentration is expressed as a solution's pH.

Explain the properties of carbon that make it the chemical basis of all life.

Describe the variety and chemical characteristics of common functional groups of organic compounds.

Diagram how small molecules may be assembled into larger ones by dehydration reactions and how hydrolysis reactions can reverse this process.

List the four major classes of organic molecules and macromolecules found in living organisms

If shown a molecule, tell whether it is organic or not and how you know.

If shown an organic molecule, tell whether it is an amino acid, nucleotide, fatty acid, steroid, monosaccharide or disaccharide and how you know.

Distinguish among different forms of carbohydrate molecules, including monosaccharides, disaccharides, and polysaccharides.

Relate the functions of plant and animal polysaccharides to their structure.

List the several different classes of lipid molecules important in living organisms.

Diagram the structure of a triglyceride and explain how it is affected by the presence of saturated and unsaturated fatty acids. Explain why some fats are solid at room temperature, and others are liquid.

Discuss how fats function as energy-storage molecules.

Apply knowledge of the structure of phospholipids to the formation of cellular membranes.

Describe the chemical nature of steroids and give an example of their biological importance.

Give examples of the general types of functions that are carried out in cells by different types of proteins.

Explain how amino acids are joined to form a polypeptide, and distinguish between a polypeptide and protein.

Describe the levels of protein structure and the factors that determine them. If shown a protein diagram, label parts that represent its levels of structure. Tell what kind of research techniques are used to determine protein structure.

Outline the bonding forces important in determining protein shape and function.

Explain what domains are and their importance in proteins.

Describe the three components of nucleotides.

Distinguish between the structures of DNA and RNA.

Tell how certain bases pair with others in DNA and RNA.

Discuss the 4 major categories of organic macromolecules found in living things, including structure, function and location of each.

Compare and contrast the general structural features of prokaryotic and eukaryotic cells.

Outline the differences in complexity among bacteria, animal, and plant cells.

Describe how a eukaryotic cell can be viewed as four interacting systems: the nucleus, cytosol, endomembrane system, and semiautonomous organelles.

Explain how the proteome underlies the structure and function of cells.

Analyze how cell size and shape affect the surface area/volume ratio.

Identify the location of the cytosol in a eukaryotic cell and list its general functions.

Describe the three types of protein filaments that make up the cytoskeleton. Identify which underlie cilia, flagella, centrioles, the nuclear lamina, and the brush border. Tell which are readily assembled and disassembled. Tell which are involved in various cell shape changes or movements.

Explain how motor proteins interact with microtubules or actin filaments to promote cellular movement.

Describe the structure and organization of the cell nucleus. Describe the structure and function of nuclear pores.

Outline the structures and general functions of the components of the endomembrane system.

Distinguish between the rough endoplasmic reticulum and the smooth endoplasmic reticulum.

Identify three important functions of the plasma membrane.

Tell why mitochondria and chloroplasts are called semi-autonomous organelles.

Discuss the evidence for the endosymbiosis theory.

Outline the structures and general functions of mitochondria and chloroplasts.

Explain how proteins are moved via vesicles through the endomembrane system.

If you are told about the function of a specific protein, tell where and in what type of cell that protein might be found.

Sketch and label a “typical” animal cell and a real animal cell such as a red blood cell or a muscle cell. Tell how it might be different than the “typical” cell in terms of its organelles and shape.

Sketch and label a “typical” plant cell and a real plant cell such as a root or leaf cell. Tell how it might be different than the “typical” cell in terms of its organelles and shape.

Describe the fluid-mosaic model of membrane structure. Tell why membranes are described as “fluid mosaics”.

Draw 10 phospholipid molecules as they would be arranged in a bilayer. Label the hydrophobic and hydrophilic parts.

61. Name all the places in a cell where membranes are found.

62. Describe at least three different categories of membrane proteins and tell what they do.

63. Describe what determines how fluid membranes are.

64. Explain how lipids are synthesized at the ER membrane.

65. Explain how transmembrane proteins are inserted into the ER membrane.

66. Compare and contrast diffusion, facilitated diffusion, passive transport, and active transport.

67. Explain the process of osmosis and how it affects cell structure.

68. Outline the functional differences between channels and transporters. Compare and contrast uniporters, symporters, and antiporters.

69. Explain the difference between primary active transport and secondary active transport.

70. Describe the structure and function of the sodium-potassium pump in animal cells and a similar pump in plants and prokaryotes.

71. Describe exocytosis and endocytosis and tell what molecules are moved across the membrane by these.

Discuss membrane transport, including its function and various forms and why all membranes have each form.

73. If a given cellular process is described, tell which form of transport might be involved.

List the different categories of animal tissue, providing general functions and specific examples of each.

Name the various organ systems found in many animals, list the components of each, and describe their general functions.

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