1. Introduction to Biology

2. Chemistry

3. Water

4. Biomolecules

5. Cell Components

6. The Membrane

7. Energy and Metabolism

8. Respiration

9. Photosynthesis

10. Cell Signaling

11. Cell Division

12. Meiosis

13. Mendelian Genetics

14. DNA Synthesis

15. Gene Expression

16. Regulation of Expression

17. Viruses

18. Biotechnology

19. Genomics

20. Development

21. Evolution by Natural Selection

22. Evolution of Populations

23. Speciation

24. History of Life on Earth

25. Phylogeny

26. Prokaryotes

27. Protists

28. Plants

29. Fungi

30. Overview of Animals

31. Invertebrates

32. Vertebrates

33. Plant Anatomy

34. Vascular Plant Transport

35. Soil

36. Plant Reproduction

37. Plant Sensation and Response

38. Animal Form and Function

39. Digestive System

40. Circulatory System

41. Immune System

42. Osmoregulation and Excretion

43. Endocrine System

44. Animal Reproduction

45. Nervous System

46. Sensory Systems

47. Muscle Systems

48. Ecology

49. Animal Behavior

50. Population Ecology

51. Community Ecology

52. Ecosystems

53. Conservation Biology

[BOOK BIO] CLUTCH

HHMI BioInteractive: Differentiation and the Fate of Cells

PROCESS OF SCIENCE Explain why researchers formulate a null hypothesis in addition to a hypothesis when designing an experimental study.

Apoptosis: Programmed Cell Death

How Cells Become Specialized

Organization and Symmetry in Kingdom Animalia

Cell differentiation always involves
a. transcription of the myoD gene.
b. the movement of cells.
c. the production of tissue-specific proteins.
d. the selective loss of certain genes from the genome.

Introduction to Animal Development

The Evolution of Hox Genes

Dorsal Ventral Polarity Generation in Drosophila | Gurken-Torpedo Pathway

No. The DNA in every cell in a multicellular organism is essentially the same.

exchange DNA with other cells via the process of horizontal gene transfer

No. Horizontal gene transfer is most common in prokaryotes. It is not a part of differentiation.

gain and lose genes, depending on what type of cell they will become

randomly turn on and off genes until the right combination is reached

No. Gene expression during differentiation is tightly controlled.

express different genes in response to developmental signals

Why is a muscle cell different from a nerve cell?

During the process of differentiation, cells __________.

Animation: Apoptosis

Type I diabetes is a form of diabetes that is due to the loss of insulin-producing cells of the pancreas. The potential of stem cells—in particular, induced pluripotent stem (iPS) cells—for therapy has gotten a lot of press.

If researchers were attempting to stimulate the differentiation of iPS cells, which of the following would they most likely add to the cell-culture medium (the liquid surrounding the cells)?
a. activin A, an extracellular signal protein
b. Sox-2, a transcription factor active in early development
c. Grb-2, an intracellular signal transduction protein
d. lactase, an enzyme that catalyzes the breakdown of lactose

Apoptosis | Cell division | Biology | Khan Academy

Early embryogenesis - Cleavage, blastulation, gastrulation, and neurulation | MCAT | Khan Academy

Eukaryotic Regulation of Gene Expression

HHMI BioInteractive: The Making of the Fittest: Evolving Switches, Evolving Bodies

Which of the following provides the strongest evidence for the conservation of tool-kit genes?
a. Bicoid moved from one fly embryo into the posterior of another fly embryo causes the formation of two head regions.

b. Mutation of an unrelated gene in another species of fly has a similar effect to mutation of bicoid in Drosophila.

c. A mouse Hox gene can be used to take over the function of a mutated Drosophila Hox gene.

d. Sheep can be cloned by fusing a differentiated adult cell with an enucleated egg.

Drosophila Embryogenesis - Anterior/Posterior Patterning [English Captions]

No. Differentiation is the expression of a cell's determined state.

No. Determination occurs when a cell's developmental fate is fixed.

No. Transduction occurs when energy is converted from one form to another.

No. Apoptosis refers to a form of programmed cell death.

This process involves cell signaling.

Cells can influence each other's development by a process known as __________.

Some stickleback fish develop protective spines, and other stickleback fish are spineless. Spine development is controlled by the expression of a gene known as Pitx1. The spineless phenotype is due to a mutation in Pitx1 that results in no expression of Pitx1 during development in regions where spines would otherwise form. When scientists compared the Pitx1 coding sequence in spined and spineless fish, they found this sequence was the same in both types of fish. Propose plausible hypotheses for the location of this mutation and for how it alters spine development.

Scientists have recently developed a process by which a skin cell from a human can be triggered to develop into a human heart muscle cell. This is possible because                   .
a. most cells in the human body contain the genetic instructions for making all types of human cells;
b. a skin cell is produced when all genes in the cell are expressed; turning off some genes in the cell results in a heart cell;
c. scientists can add new genes to old cells to make them take different forms;
d. a skin cell expresses only recessive alleles, so it can be triggered to produce dominant heart cell alleles;
e. it is easy to mutate the genes in skin cells to produce the alleles required for other cell types

Absence of bicoid mRNA from a Drosophila egg leads to the absence of anterior larval body parts and mirror-image duplication of posterior parts. This is evidence that the product of the bicoid gene
a. normally leads to formation of head structures.
b. normally leads to formation of tail structures.
c. is transcribed in the early embryo.
d. is a protein present in all head structures.

No. This gene is involved in development in mammals.

No. Hox genes are involved in pattern formation.

No. Morphogens are proteins, not nucleic acids.

No. TATA is a sequence in gene promoters.

These sequences are named for the kind of gene in which they are found.

The highly conserved sequence element present within homeotic genes is called the __________.

What is apoptosis?
a. an experimental technique used to kill specific cells

b. programmed cell death that is required for normal development

c. a pathological condition observed only in damaged or diseased organisms

d. a developmental mechanism unique to the roundworm C. elegans

A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of
a. the influence of environment on development.
b. paedomorphosis.
c. a change in a developmental gene or in its regulation that altered the spatial organization of body parts.
d. heterochrony.

Symmetry in Animals | Types of Symmetry | Kingdom Animalia

In adult animals,            are a source of undifferentiated cells that can divide to produce cells that can specialize.

Animation: Role of bicoid Gene in Drosophila Development

What is the connection between genetic regulatory cascades and the observation that differentiation is a step-by-step process?

Hox genes and the evolution of animal body plans

The science of symmetry - Colm Kelleher

Development of Embryo | Reproduction in Animals | Don't Memorise

Introduction: Morphogens

DRAW IT Each blue circle in the figure below represents a cell in a cell lineage. Draw two modified versions of the cell lineage so that each version produces three cells. Use apoptosis in one of the versions, marking any dead cells with an X.

Short Video: Phosphate induced Apoptosis

The cytoskeleton inhibits cell migration.

No. The cytoskeleton is responsible for cell migration.

The extracellular matrix is not involved in the migration of cells.

No. The extracellular matrix can direct the migration of cells.

Cell adhesion molecules are secreted glycoproteins found in the extracellular matrix.

No. Cell adhesion molecules are transmembrane glycoproteins.

Cell adhesion molecules are located inside cells.

No. Cell adhesion molecules are located on cell surfaces.

Cells reach specific destinations through the action of cell adhesion molecules and the extracellular matrix.

Recall the role of cell adhesion molecules in cell migrations.

Which of the following statements is true?

Some humans have genes that make them resistant to infection by HIV. Would human populations likely evolve differently in areas of the world where HIV infection rates are high? Explain your logic.

Pattern Formation

What does it mean to say that a characteristic is heritable?
a. The characteristic evolves.
b. The characteristic can be passed on to offspring.
c. The characteristic is advantageous to the organism.
d. The characteristic does not vary in the population.

Developmental Biology

What are homeobox genes?

Eukaryotic Gene Regulation Video 2 (Post-transcriptional)

No. The probability of this occurring is very small.

No. Analogy is similarity due to convergence in evolution.

that it is not responsive to natural selection

No. The conservation of the homeobox sequence indicates that selection has acted to eliminate variants.

No. If the homeobox arose recently, it would be shared by fewer kinds of organisms. It might even be unique to a specific group.

of the common ancestry of different life-forms

This is an example of homology. (You will learn more about homology in Chapter 22.)

The similarity of the homeobox in many different kinds of organisms is evidence __________.

Symmetry in Animals

Could both the food competition hypothesis and the sexual competition hypothesis explain why giraffes have long necks? Why or why not?

Chapter 36   Animal Development

Which of the following occurs when a covalent bond forms?
a. Electrons in valence shells are transferred from one atom to another.
b. Electrons in valence shells are shared between atoms.
c. Partial charges on polar molecules interact.
d. Nonpolar molecules are pushed together.by surrounding water molecules.

Why Are Animals Symmetrical?

Eukaryotic Gene Regulation part 1

Gene Silencing by microRNA

Evolutionary Development: Chicken Teeth - Crash Course Biology #17

Morphogenesis in animals and plants involves the movement of cells.

No. Morphogenesis in animals, but not plants, involves the movement of cells.

Cells do not migrate individually. Instead, they migrate as a sheet.

No. Sometimes cells migrate individually, and other times they migrate as a sheet.

During cleavage, gastrulation, and organogenesis, cells do not change shape.

No. During cleavage, gastrulation, and organogenesis, cells change shape.

During cleavage, gastrulation, and organogenesis, cells do not change position.

No. During cleavage, gastrulation, and organogenesis, cells change position.

Microtubules and actin filaments played a crucial role in your early development.

Morphogens Vs Signals

The following predictions ask you to consider how genetic regulatory cascades provide positional information. Select True or False for each statement.
T/F Mutation of a gene at one level of a regulatory cascade will affect the expression of genes at all levels of the cascade.
T/F Mutation of a gene that is expressed later in a regulatory cascade will affect a smaller region of the body than mutation of gene that is expressed early in the cascade.
T/F In the regulatory cascade used by Drosophila, a gene at one level of the cascade will be controlled only by genes at the level immediately above it.
T/F Genes that control the largest regions of the Drosophila embryo are not transcribed in the embryo.

Your bone cells, muscle cells, and skin cells look different because
a. each cell contains different kinds of genes.
b. they are present in different organs.
c. different genes are active in each kind of cell.
d. they contain different numbers of genes.

Embryo Development in Animals.wmv

SYMMETRICAL AND ASYMMETRICAL ANIMALS

Morphogen gradient scaling during tissue growth

No. Apoptosis is the term for programmed cell death.

a failure involving post-transcriptional modification of mRNA

No. There is no evidence to indicate that this condition arises from problems with modifications of mRNA.

destruction of the RNA polymerase molecules responsible for the transcription of genes that encode head-related proteins

No. Destruction of RNA polymerase molecules would affect transcription of all genes.

What genes provide positional information?

Instead of developing a head and a tail, an abnormal Drosophila embryo develops two tails. This is most likely due to __________.

HHMI BioInteractive: Creating Embryonic Stem Cell Lines

What did Linnaeus' system of naming organisms ensure?
a. Two different organisms never end up with the same genus and species name.
b. Two different organisms have the same genus and species name if they are closely related.
c. The genus name is different for closely related species.
d. The species name is the same for each organism in a genus.

a cell appears different under the microscope

No. Cell differentiation is observable even before the cell begins to undergo changes in structure that are observable under a microscope.

No. A cell's genome does not usually change. The expression of the genes in the genome changes as a cell differentiates.

patterns of mitosis change in different cells

No. The process of mitosis is the same for all cells.

mRNAs for tissue-specific proteins appear in a cell

We are able to observe some subtle things that are occurring in cells.

Cell differentiation is first observable when __________.

Which of the following is a valid difference between embryonic stem cells and the stem cells found in adult tissues?
a. In laboratory culture, only adult stem cells are immortal.
b. In nature, only embryonic stem cells give rise to all the different types of cells in the organism.
c. Only adult stem cells can differentiate in culture.
d. Embryonic stem cells are generally more difficult to grow in culture than adult stem cells.

Cellular specialization (differentiation) | Cells | MCAT | Khan Academy

A friend is interested in isolating genes that are expressed solely in liver cells but only has access to skin cells. She asks you for advice on whether to start her studies. What will you say?

HHMI BioInteractive: Somatic Cell Nuclear Transfer Animation

Differential Expression, Morphogens, and Pattern Formation

PCB 4253 Chapter 12 Part 2 Video 1   Mammalian Development Axis Specification

The equal distribution of cytoplasmic determinants and induction

No. The asymmetric distribution of cytoplasmic determinants and induction are the two main mechanisms of differentiation.

Temperature and pressure of the surrounding environment

No. Although these environmental factors influence development, they are not the mechanisms of differentiation. The uneven distribution of cytoplasmic determinants and induction are the two main mechanisms of differentiation.

No. One of the listed responses is correct.

The uneven distribution of cytoplasmic determinants and induction

These mechanisms cause genetically similar cells to develop differently.

What are the two main genetic and cellular mechanisms that underlie differentiation?

Type I diabetes is a form of diabetes that is due to the loss of insulin-producing cells of the pancreas. The potential of stem cells—in particular, induced pluripotent stem (iPS) cells—for therapy has gotten a lot of press.

What are iPS cells?
a. cells taken from early human embryos

b. cells taken from the pancreas of people without diabetes

c. cells derived by de-differentiating specialized adult cells

d. cells derived by differentiating pancreas precursor cells

Gene Regulation: Hox Genes | A-level Biology | OCR, AQA, Edexcel

Axis Formation in Drosophila

Apoptosis and Cell Communication

Apoptotic Pathways

Imagine a situation in which a morphogen has its source at the posterior end of a Drosophila embryo. Every 100 µm from the posterior pole, the morphogen concentration decreases by half. If a cell required 1/16th the amount of morphogen found at the posterior pole to form part of a leg, how far from the posterior pole would the leg form?
a. 100 μm

b. 160 μm

c. 400 μm

d. 1600 μm

act by binding to a plasma protein receptor that then initiates a signal-transduction pathway

No. Cytoplasmic determinants are stored in egg cells by the mother before fertilization.

Where are cytoplasmic determinants located, and when do they get there?

Cytoplasmic determinants __________.

Body Axes

What is 'selected' during natural selection? Explain your answer.

No. Heterozygous and homozygous refer to the alleles of a particular gene.

No. Totipotent cells can give rise to any type of cell, but nerve cells are completely differentiated.

What are the two basic types of stem cells?