Bio 152 Week 7 Study Guide

What types of molecules are used by complex multicellular organisms to attach cells to each other?

(proteins like cadherin and adhesinprotein-carbohydrate complexes) - Glycoprotein is just a fancy (scientific name) for molecules that contain both proteins and carbohydrates (sometimes they are called proteoglycan complexes is there are a lot of components) glycoproteins proteins carbohydrates

In simple multicellular organisms, what is the most likely way for them to acquire nutrients?

** Each cell transports its own nutrients Remember, most if not all cells in simple multicellular organisms are in direct contact with the surrounding environment. There is little to no cellular differentiation in simple multicellular organisms. This is in part due to the fact that each cell is in direct contact with the surrounding environment and each cell is capable of all of the functions of a cell. **Cellular differentiation is the process in which a cell changes from one cell type to another. Usually, the cell changes to a more specialized type.**

Compare and contrast the roles of plasmodesmata and gap junctions in cell communication

- Communication is important during development, guiding the patterns of gene expression that differentiate cells, tissues, and organs - Cells communicate using signaling molecules (generally a protein) synthesized by one cell which binds with a receptor protein on the surface of a second cell. ** This interaction can essentially flip a molecular switch that activates or represses gene expression in the receptor cell's nucleus or stimulates another response from the receiving cells. - Molecular evidence indicates that many of the signaling pathways used for communication between cells in complex multicellular organisms first evolved in single-celled eukaryotes. - Plants, in contrast, have intercellular channels are lined by extensions of the cell membrane - Tubules running through these channels connect the endomembrane systems of the two cells. - Like gap junctions, plasmodesmata permit signaling molecules to pass between cells in such a way that they can be targeted to only one or a few adjacent cells. ** Complex red and brown algae also have plasmodesmata, and complex fungi have pores between cells that enable communication by means of cytoplasmic flow - As similar channels do not occur in most other eukaryotic organisms, they appear to represent an important step in the evolution of complex multicellularity. ** cell to cell communication in plants occurs through plasmodesmata; this connection serves a similar function to the gap junctions found in animal cells** - All cells have transmembrane receptors that respond to signals from the environment. In some cases, the signal is a molecule released by a food organism (such as the bacteria that induce simple multicellularity in choanoflagellates), and in some cases the cells sense nutrients, temperature, or oxygen level. - Single celled eukaryotes also communicate with other cells within the same species, for example to ensure that two cells can find each other to fuse in sexual reproduction. Signaling between two cells within a complex multicellular organism (plant, animal or fungal) can be seen as a variation on this more general theme of a cell responding to other cells and the physical environment. - complex multicellular organisms have distinct cellular pathways for the movement of molecules from one cell to another - animals are more complex than sponges have gap junctions, protein channels that allow ions and signaling molecules to move from one cell into another ** Gap junctions not only help cells to communicate with their neighbors, they allow targeted communication between a cell and specific cells adjacent to it.** Plasmodesmata are channels between adjacent plant cells, while gap junctions are channels between adjacent animal cells. However, their structures are quite different At plasmodesmata, the plasma membranes of adjacent plant cells are continuous, and the cells share portions of the smooth endoplasmic reticulum. Gap junctions connect adjacent animal cells by forming protein-lined pores. Both structures are openings between cells that allow cytosol, including ions and small molecules, to be shared.

List and describe the key characteristics of Eukaryotes

- Eukaryotes have at least one internal membrane bound structure (the nucleus) - Data from these fossils have led comparative biologists to the conclusion that living eukaryotes are all descendants of a single common ancestor. - the indication is that there was a common ancestor at some point that had the following characteristics: 1. A nucleus (or nuclei) surrounded by a nuclear envelope with nuclear pores. 2. Mitochondria, with two separate membranes and a chromosome separate from those found in the nucleus 3. A cytoskeleton containing the structural and motility components called actin microfilaments and microtubules. 4. Flagella and cilia, organelles associated with cell motility. 5. Chromosomes, each consisting of a linear DNA molecule coiled around basic (alkaline) proteins called histones. 6. Mitosis, a process of nuclear division wherein replicated chromosomes are divided and separated using elements of the cytoskeleton. Mitosis is universally present in eukaryotes. 7. Sexual reproduction, a process of genetic recombination unique to eukaryotes in which diploid nuclei at one stage of the life cycle undergo meiosis to yield haploid nuclei and a subsequent stage where two haploid nuclei fuse together to create a diploid zygote nucleus. - Eukaryotic cells are differentiated from prokaryotic cells by a variety of features, one of which is the presence of internal membrane bound structures (ex:nucleus, mitochondria, chloroplasts) - The process of aerobic respiration is found in all major lineages of eukaryotes, and it is localized in the mitochondria in these **some prokaryotes began using energy from sunlight to power anabolic processes that reduce carbon dioxide to form organic compounds. That is, they evolved the ability to photosynthesize.** Hydrogen, derived from various sources, was captured using light-powered reactions to reduce fixed carbon dioxide in the Calvin cycle. The group of Gram-negative bacteria that gave rise to cyanobacteria used water as the hydrogen source and released O2 as a waste product. - Various metabolic processes evolved that protected organisms from oxygen, one of which, aerobic respiration, also generated high levels of ATP - Recall that the first fossils that we believe to be eukaryotes date to about 2 billion years old, so they appeared as oxygen levels were increasing - recall that all extant eukaryotes descended from an ancestor with mitochondria.

Describe how cell differentiation can be accomplished in complex multicellular organisms

- In multicellular organisms, growth and development is the result of molecular communication between cells. - A signal commonly alters the production of proteins-inducing the reorganization of the cytoskeleton, for example. As a result, a stem cell may become an epithelial cell, or a muscle cell, or a neuron - What causes the same gene to be turned on in one cell and off in another? ** The ultimate answer is that two cells in the same developing organism can be exposed to very different environments. - stem cells can differentiate in one of three different categories of cells that sub-divide into specific cell types and roles (differentiation is controlled by cell position and chemical signals) - . Many unicellular organisms have life cycles in which different cell types alternate in time, depending on environmental conditions. For example, if we experimentally starve dinoflagellate cells, two cells undergo sexual fusion to form morphologically and physiologically distinct resting cells protected by thick walls. That is, a nutrient shortage induces a change in gene expression that leads to the formation of resting cells. When food becomes available again, the cells undergo meiotic cell division to form new feeding cells. Many other single-celled eukaryotes form resting cells in response to environmental cues, especially deprivation of nutrients or oxygen - Usually, the cell changes to a more specialized type. Differentiation occurs numerous times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types. ... Some differentiation occurs in response to antigen exposure. - Differentiation and specialization is necessary in multicellular organisms because maintaining a full complement of all cellular capabilities is costly and/or incompatible with meeting all the organism's needs. Groups of specialized cells cooperate to form a tissue, such as a muscle. - When cells express specific genes that characterise a certain type of cell we say that a cell has become differentiated. Multicellular organisms must therefore retain some unspecialised cells that can replenish cells when needed. ... These unspecialised cells are called stem cells. - Cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of tissues and cell types

Describe the evidence that supports the evolution of simple multicellularity in some protists

- In your own body, for example, different cells are specialized for specific functions, so that while your body as a whole can perform the broad range of tasks accomplished by microorganisms, individual cells for the most part cannot - To date, cadherins have been found only in choanoflagellates and animals, but proteins of the integrin complex extend even deeper into eukaryotic phylogeny-they are found in single celled protists that branch near the base of the opisthokont superkingdom. - By having multiple connect cells that function together organisms may be able to escape predation, improve ability to acquire nutrients, stabilize themselves in the environment and ultimately reproduce more successfully. - Regardless of the mechanism, all these organisms share the features, that each cell retains full function and is in direct contact with the environment. This separates these organisms from more complex multicellular organisms which displays cell differentiation and have cells that isolated from direct environmental contact.

What features do all eukaryotes share that are not found in prokaryotes?

- Mitochondria or at least evidence of having had mitochondria - linear DNA molecule(s) coiled around histone proteins (or evidence of this at one time) - A cytoskeleton of actin microfilaments and microtubules

Explain the advantages of simple multicellularity

- One selective advantage is that multicellularity helps organisms avoid getting eaten. - in the presence of the predators, within 10 to 20 generations, most of the algae were living in eight-cell colonies that were essentially invulnerable to predator attack due to their larger size. - Another advantage is that multicellular organisms may be able to maintain their position on a surface or in the water column better than their single-celled relatives. - Seaweeds, for example, live anchored to the seafloor in places where light and nutrients support growth. When exposed to consistent shaking in culture, the number of cells that formed aggregates (clumps) increase over a number of generations. By clumping together the cell groups settled on the bottom of the cultures and thus were exposed to less vigorous conditions. - Feeding provides a third potential advantage: In colonial heterotrophs such as the stalked ciliate Epistylis , the coordinated beating of flagella assists feeding by directing currents of food-laden water toward the cells ** a link between the presence of the prey species and the development of multicellular colonies (formation of a rosette). These colonies, unlike the ones in the yeast and algae mentioned earlier, appear to the result of cell division rather than cell aggregation

Discuss adaptations needed for simple multicellularity

- The genome of the choanoflagellate Monosiga brevicollis provides fascinating insight into the evolution of cell adhesion molecules. Choanoflagellates, the closest protistan relatives of animals, are unicellular microorganisms. Therefore, it came as a surprise that the genes of M. brevicollis code for many of the same protein families that promote cell adhesion in animals. - This includes the genes for both cadherin and integrin proteins which in animals are involved in supporting epithelia. - One approach to an answer came from the observation that cells stick not only to one another but also to rock or sediment surfaces - Proteins that originally evolved to promote adhesion of individual cells to sand grains or a rock surface may have been modified during evolution for cell-cell adhesion - it is also possible that adhesion molecules were originally used in the capture of bacterial cells, to make prey adhere to the predator. - Such a phylogenetic distribution provides strong support for the general hypothesis that cell adhesion in animals resulted from the redeployment of protein families that evolved to perform other functions before animals diverged from their closest protistan relatives.

Describe the evolutionary consequences of complex multicellularity

- With these requirements in place, natural selection would favor the increase and diversification of genes that regulate growth and development, making possible more complex morphology and anatomy. - functional key to complex multicellularity: the differentiation of tissues and organs that govern the bulk flow of fluids, nutrients, signaling molecules, and oxygen through increasingly large and complex bodies. - This differentiation freed organisms from the tight constraints imposed by diffusion. When all these features are placed onto phylogenies, they show both the predicted order of acquisition and the tremendous evolutionary consequences of complex multicellularity 1. Highly developed mechanisms for adhesion between cells 2. Specialized structures for cell communication 3. Tissue and organ differentiation 4. A small subset of cells contribute to reproduction 5. Cell or tissue loss can be lethal for the organism 6. Presence of both interior and exterior cells- These are common characteristics of most complex multicellular organisms. - A multicellular organism needs more food than unicellular organsism because it needs more energy. In multicellular organisms, cells are organized into tissues and tissues are further organised into organs. So, if one organ fails, then whole organism can fail. - Multicellular organisms, especially long-living animals, also face the challenge of cancer, which occurs when cells fail to regulate their growth within the normal program of development. - Simple multicellularity has evolved numerous times within the Eukarya, but complex multicellular organisms belong to only six clades: animals, em- bryophytic land plants, florideophyte red algae, laminarialean brown algae, and two groups of fungi.

Explain the evidence that supports the theory of endosymbiosis

- appeared to be somewhat worm-shaped structures that seemed to be moving around in the cell. - eukaryotes were believed to be some kind of bacteria living in host cells but these hypotheses remained unknown or rejected in most scientific communities. - Margulis noted that the mitochondria, a compartment within the cell that generated the energy required for metabolism, looked remarkably like a bacteria - Some even suggested that mitochondria began from bacteria that lived in a permanent symbiosis within the cells of animals and plants. - Additionally, algae and plant cells have a second set of bodies (chloroplasts) that they use to carry out photosynthesis. - chloroplasts and mitochondria have high resemblances to bacteria - chloroplasts, like mitochondria, evolved from symbiotic bacteria — specifically, that they descended from cyanobacteria, the light-harnessing small organisms that abound in oceans and freshwater. - Broadly, it has become clear that many Eukaryotic nuclear genes and the molecular machinery responsible for DNA replication and gene expression appear to be more closely related to those in Archaea, rather than bacteria - the metabolic organelles (mitochondria, chloroplasts) and genes responsible for many energy-harvesting processes appear to have their origins in bacteria - - Endosymbiosis involves one cell engulfing another to produce, over time, a coevolved relationship in which neither cell could survive alone. - It was aerobic because it had mitochondria that were the result of an endosymbiosis involving an aerobic prokaryote. Whether this early eukaryote had a nucleus at the time of the initial symbiosis remains unknown.

Differentiate between simple multicellularity and similar adaptations that are not considered simple multicellularity

- cell adhesion molecules cause adjacent cells to stick together, but there are few specialized cell types and relatively little communication or transfer of resources between cells. - Most or all of the cells in simple multicellular organisms retain a full range of functions, including reproduction. As a result the organism/colony usually pays only a small penalty for individual cell death - in simple multicellular organisms, nearly every cell is in direct contact with the external environment, at least during phases of the life cycle when the cells must acquire nutrients, which means that each can take up nutrients and excrete wastes directly. - While simple multicellularity has evolved in numerous groups of protists (typically single celled eukaryotes) there are some groups that have achieved a temporary simple multicellularity by a different route, aggregating during just one stage of the life cycle. Slime molds are the best-known example ** cellular slime molds can alternate between single free living amoeboid cells and a simple multicellular form (slug) -- in response to environmental conditions - In these groups, environmental conditions can result in signaling that causes single cells to aggregate and join together to form a larger colony to help survive. - in cellular slime molds the colony is mobile and when conditions become favorable the cells will undergo differentiation to form a structure for spore (single cell) dispersal. Other slime molds (acellular) have adapted to undergo mitosis without the resulting cell division. -- This creates a larger cell that has multiple nuclei (coenocytic) ** While not truly multicellular this organism does function like a simple multicellular organism as each region of the large cell (can be visible to the naked eye) is able to respond locally to conditions.** - There are numerous organisms that have evolved similar mechanisms to bring cells together to work in unity, including cell aggregation in response to environmental stimuli in cellular slime molds and large multinucleate cells in acellular slime molds.

Describe the evidence to support second endosymbiosis of plastids

- while some currently existing eukaryotes have very reduced remnants of mitochondria in their cells, all eukaryotes have mitochondria - Plants, algae and some single celled eukaryotes are unique in that they have both mitochondria and chloroplasts - While chloroplasts could also have evolved through endosymbiosis, the fact that these cells also contain mitochondria seems to indicate that perhaps two separate events may have occurred. 1. infoldings in the plasma membrane of an ancestral prokaryote gave rise to the endomembrane components, including a nucleus and endoplasmic reticulum 2. in the first endosymbiotic event, ancestral eukaryote consumed aerobic bacteria that evolved into mitochondria 3. second endosymbiotic event, early eukaryote consumed photosynthetic bacteria that evolved into chloroplasts 4. modern mitochondrion and photosynthetic eukaryote ** Molecular and morphological evidence suggest that the eukaryote chlorarachniophytes (a green algae) may have arisen from a secondary endosymbiotic event.** - possibility of a cell containing an endosymbiont to itself become engulfed, resulting in a secondary endosymbiosis - Within the cells of this algae are structures that have four membranes, 1. the two that make up the inner and outer membranes of the chloroplast, 3. a membrane that surround the chloroplast that appears to be of green alga origin 4. and a fourth that is likely to correspond to the vacuole used to surround the alga and bring it into the cell. - within the membranes there is also evidence of a vestigial nucleus **Secondary Endosymbiosis occurs when the host cell in primary Endosymbiosis is itself engulfed by another cell. This process is illustrated in the diagram above. A green algae, which descended from the product of primary Endosymbiosis, is engulfed by a larger heterotrophic cell. The green algae then becomes a red algae inside the host cell by losing the nucleus and mitochondria that had been present before the algae engaged in primary Endosymbiosis. The result is a double membrane bound organelle containing all the structures necessary for photosynthesis. Over time these red algae evolved to become the plastids known as chloroplasts.** The inner layer is the membrane originally containing the photosynthetic bacteria that was engulfed in primary Endosymbiosis, and the second layer is the membrane of the original host cell that was in turn engulfed by the final heterotroph. - In other related green algae that are thought to be involved secondary endosymbiosis, only three membranes can be identified around plastids. The current theory is that a sequential loss of a membranes occurred during the course of evolution.

How do simple multicellular organisms differ from more complex multicellular organisms?

-most of the cells have a full range of functions (can do all the functions) - there is relatively little communication and transfer of resources between cells -every cell is in direct contact with the external environment at some point Remember that in simple multicellular organisms each cell retains all of the functions of all of the cells. In complex multicellular organisms there are specialized cells with specialized functions. - loss of a single cell has more of an impact on complex multicellular

Explain the order of acquisition of multicellular traits

-organelle, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystem, and biosphere. - The innovation of complex multicellularity was to differentiate cells in space instead of time -In a three-dimensional multicellular organism, only surface cells are in direct contact with the outside environment. - Interior cells are exposed to a different physical and chemical environment because nutrients, oxygen, and light become less abundant with increasing depth within tissues. - In effect, there is a gradient of environmental signals within multicellular organisms. - in the earliest organisms with three-dimensional multicellularity, a nutrient or oxygen gradient triggered oxygen- or nutrient-starved interior cells to differentiate, much as happens to trigger the formation of resting cells in their single-celled relatives. - With increasing genetic control of cellular responses to signaling gradients, the seeds of complex development were sown. - Bulk flow, which transports nutrients, oxygen, and water within complex multicellular organisms, also carries developmental signals - Signals carried by bulk flow can travel far greater distances through the body than signals transmitted by diffusion alone - For example, in animals the endocrine system releases hormones directly into the bloodstream, enabling them to affect cells far from those within which they formed. Thus, the sex hormones estrogen and testosterone are synthesized in reproductive organs but regulate development throughout the body, contributing to the differences between males and females. In this way, signals carried by bulk flow can induce the formation of distinct cell types and tissues along the path of signal transport **These three requirements had to be acquired in a specific order.** - complex multicellular organisms require mechanisms for cell adhesion, - modes of communication between cells, - and a genetic program to guide growth and development. - If the products of cell division don't stick together, there can be no complex multicellularity. Adhesion, however, is not sufficient. It must be followed by mechanisms for communication between cells. Moreover, cells must be able to send molecular messages to specific targets or regions, assisted in animals by gap junctions and in plants by plasmodesmata.

In what order are the following thought to have evolved to have given rise to complex multicellularity?

1. ability of cells to divide 2. ability of cells to stick together (cell adhesion) 3. ability of cells in groups to communicate through signalling 4. the formation of structures to facilitate cell signalling Cell division (mitosis and binary fission) appear in single celled organisms, so it was an early evolutionary process.

Which of the following BEST describes the flow of information in a cell?

DNA to RNA to proteins

Simple multicellularity can be the result of cell aggregation (cells sticking together) but not the result of cell division (cell cloning).

False Cell aggregation allows cells to bind to other cells (not necessarily all the same cell), while cell division (cloning) can result in a cluster of the same cells. Either of the mechanisms can play a role in the development of simple (and later complex) multicellularity. Since multicellularity arose independently in different lineages, the mechanism is likely to have varied.

How does cell differentiation differ between unicellular and complex multicellular organisms?

Multicellular organisms have a spatial differentiation of cells Unicellular organisms are made up of only one cell that carries out all of the functions needed by the organism, while multicellular organisms use many different cells to function. ... Multicellular organisms are composed of more than one cell, with groups of cells differentiating to take on specialized functions

The nucleus, endoplasmic reticulum, golgi and plasma membrane are all part of the endomembrane system, this means that they all?

Share the same membrane - These membranes all share some key phospholipids and other components as each is physically connected to the other either directly or through the movement of vesicles.

A cell that is actively involved in exchanging a lot of material with their surroundings would be expected to have?

a larger surface to volume ratio surface to volume ratios are fraction (ugh, yes I know). So if the surface area (numerator) is larger than the volume (denominator) the value will be bigger than if the surface area is smaller than the volume. Active cells need a large surface area in order to be able to bring in enough food/energy to maintain growth.

What do all complex multicellular organisms have in common?

a means by which to hold cells together highly developed cell-cell communication regulatory gene networks that control cell and tissue differentiation patterns

What do features do SIMPLE multicellular organisms have in common?

a means by which to hold cells together nearly every cell is in contact with the external solution each cell retains a full range of functions

What evidence suggests that chloroplasts were "acquired" by eukaryotic cells that already had existing mitochondria?

all eukaryotic cells have mitochondria, only some have both mitochondria and chloroplasts - Plants, algae and some single celled eukaryotes have both mitochondria and chloroplasts. All eukaryotes however have mitochondria, even those that do not have chloroplasts (animals, fungi, some single celled eukaryotes) Results for item 8. 8 1 / 1 point

Acellular slime molds undergo mitosis (duplication of nucleus) without cytokinesis (cell division). How is this likely to have evolved in this group of organisms?

as a result of a mutation in a cell division gene Remember that organisms do not change to adapt to new environmental conditions. There was likely a mutation in a gene involved in cell division that resulted in an inability of the cell to actually divide after the DNA had been replicated.

Cells can be described as having a cytoskeleton of internal structures that contribute to the shape, organization, and movement of the cell. All of the following are part of the cytoskeleton except?

cellulose - The cytoskeleton provides supporting structure for cells from the inside. It can be dynamic (it can change shape) and be involved in moving the cell as a whole and the organelles within cells.

The extracellular matrix is composed of?

collagen fibers that are attached to the membrane proteoglycans such as fibronectin integral membrane proteins, like integrin

Unlike the rigid protein framework in bacteria, a eukaryotic cell's [x] can be remodeled quickly, enabling the cell to change its shape.

cytoskeleton - Cytoskeletons in eukaryotic cells are dynamic, they can be assembled and disassembled allowing the cell to either change shape or to alter the movement of internal organelles.

Plasmodesmata in plant cells are MOST similar to which of the following structures of animal cells?

gap junctions

Discuss the role of the extracellular matrix and cell walls in cell adhesion

general requirements for complex multicellular life: (1)Cells must stick together; (2) they must communicate with one another; and (3) they must participate in a network of genetic interactions that regulates cell division and differentiation. - If a fertilized egg is to develop into a complex multicellular organism, it must divide many times, and the cells produced from those divisions must stick together - In addition, they must retain a specific spatial relationship with one another in order for the developing organism to function - animal cells produce compounds that are integrated into or attached to the plasma membrane, creating an extra cellular matrix. - primary components of these compounds are proteins, and the most abundant protein is collagen. - Collagen fibers are interwoven with carbohydrate-containing protein molecules called proteoglycans. - some cells attach themselves to this matrix by means of other transmembrane proteins called integrins and cadherins. - The extracellular matrix also allows the cells within the tissue to communicate with each other. - In plants, the cell wall connects cells together into tissues. - The plant cell wall is composed predominately of cellulose fibers which are embedded in a matrix of pectin and hemicellulose - These molecules allow plant cells to attach to each other to create the complex tissue structures that support the overall plant structure. - ungi also have cell walls, although they are composed of chitin rather than cellulose, that are involved in connecting the cells together into multicellular structures.

Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are?

hypertonic to fresh water and hypotonic to the salt solution - Rule of thumb for water movement: Hyper: more molecules, less free water Hypo: less molecules, more free water Water always moves from Hypo to hyper

A cell whose cytoplasm has a concentration of 1M glucose is placed in a test tube containing .5M glucose. Assuming that glucose is not actively transported into the cell, which of the following best describes the tonicity of the external solution relative to the cytoplasm of the cell?

hypotonic (external solution has LESS molecules going from 1 M to 0.5 M, so the inside has more water)

What are some advantages of being multicellular?

it can provide stability and help anchor the organism it can provide protection against predation It can improve movement/locomotion through coordination - Think about the benefits of a group of cells vs one lone cell. What are the advantages of working as a team?

It is thought the originally cell adhesion molecules allowed for cells to stick to surfaces. How might these molecules have evolved to become cell-cell adhesion molecules?

mutations in genes that code for adhesion molecules selection for gene products that help cells stick together Please remember that the environment does not cause favorable mutations. Mutations are random. And adaptations are the result of random mutations and selection.

Which evolutionary mechanisms are most likely to have been involved in the evolution of simple multicellularity in some eukaryotic lineages?

natural selection mutation Mutations and natural selection are the most likely mechanisms that led to the adaptations (cell adhesion and specific cell communication) necessary for simple multicellularity.

In coenocytic organisms, like acellular slime molds, _______ divides multiple times but the _____ does not. This results in a _________ cell with _________ nuclei

nucleus; cells; larger; multiple

To form colonies, cells often use ______ to attach to each other. Choanoflagelletes have genes for______ which are similar to those of animals .

proteins; cadherins Choanoflagellates are considered to share an common ancestor with the lineage that gave rise to animals. While they are single celled organisms, they do have the capacity to form colonies.

What are the underlying properties that determine plant growth and physical appearance?

regulatory network of gene expression the presence of cell walls and the nature of cell adhesion intercellular communication pathways/molecules

What characteristics do bacteria and mitochondria share?

ribosomes for protein synthesis genetic material (DNA) the ability to self-replicate a membrane composed predominately of phospholipids Mitochondria and bacteria are also very small.

Which of the following is a correct sequence for a modified/processed protein that is secreted from the cell?

rough endoplasmic reticulum - Golgi - plasma membrane

In what ways are simple multicellular organisms different from bacterial cells that live in colonies?

the cells in the simple multicellular organism are all from the same organism only some of the cells of simple multicellular organisms are involved in reproduction?? Remember that cells in simple multicellular organisms can perform all the functions that other cells do, it doesn't mean that they all do everything. Also cell differentiation is minimal in these organisms.

What two membranes in eukaryotic cells require membrane stability in order to carry out energy metabolism?

thylakoid membranes of chloroplasts mitochondrial membranes - Both the thylakoid membranes of chloroplasts and inner membranes of mitochondria have electrochemical gradient forming proteins. Thus the membrane must be stable so the gradient can form and then be used to generate ATP using ATP synthase.

In complex multicellular organisms, only a small subset of cells is usually involved in reproduction.

true

Most or all of the cells in simple multicellular organisms retain a full range of functions, including reproduction.

true

Small molecules can move from the cytoplasm of one plant cell to a neighboring cell without crossing a membrane through plasmodesmata.

true

The extracellular matrix of animal cells is involved in cell adhesion and cell communication.

true