bio module 5

Animal growth

Many animals have determinate growth, but there are fish that are indeterminate. The adult fish of one species can vary wildly in size.

Environments vary in time and space in their levels of resources and in their dangers. Summarize and describe in your own words some general differences in how animals and plants each deal with this.

-It is true that environments change over time. Animals and plants deal with this in several different ways. One way is through dispersion. Dispersion works for both animals and plants in a sense that it allows the populations to spread out within an environment. This decreases the likelihood of competing for the limited resources. However these processes look different for plants and animals. Animals are able to actively mobilize and transport themselves to new areas if they feel threatened by limited resources or other competitors. Plants are not able to do this, so they use different methods. One method involves the use of seeds. Seeds are able to disperse to new environments through wind, other animals, or water. For instance, a seed can stick to an animal which will travel away from its origin and land in a new area to grow. -Animals can often relocate themselves to a more hospitable environment, gaining more resources to fulfill their needs or escaping danger. Plants can reduce the energy they put into growth, and can even sacrifice some of their body if there is an immediate threat since they are modular and can survive even with the loss of certain structures. Plants can also grow their roots deeper and integrate with mycchorizal networks to increase their nutrient availability. They can open or close their stomata, change the direction in which they grow (towards or away from light), and possibly evolve to grow spines or toxic chemicals to deal with dangers.

Life cycle

An organism's life cycle is the series of major changes it undergoes, including reproduction, which then leads to a repetition of the life cycle. Plants have more variation at this level of detail in their life cycles than those other two kingdoms. All three kingdoms have a diploid (2n) and haploid (1n) stage in their life cycles. As part of sexual reproduction, meiosis occurs in some specialized cells of all three kingdoms: a diploid cell divides into four haploid cells.

Reproduction benefits

Asexual reproduction has some advantages, the primary one being that no mate is necessary. Yet, most eukaryotes do reproduce sexually, and so it seems that the extra complication of mating provides a significant fitness benefit. This benefit is gained because sexual reproduction increases genetic variation. Recombination occurs during meiosis, potentially creating new alleles, and those alleles are combined into a variety of genotypes during the fusion of gametes. Genetic variation in a population is also often increased by dispersal between populations.

Can you think of any other reasons why asexual reproduction may increase fitness beyond the one mentioned above?

Despite the benefits of sexual reproduction, asexual reproduction is also widespread. In some cases, just being able to have that option of reproducing without a mate provides a major benefit {this is known as reproductive assurance}. This can be particularly true of species that tend to occur at low population densities. Asexual reproduction is also often quicker than sexual reproduction. Each offspring can have offspring by itself, leading to more potential copies of that genotype. Remember that greater fitness is referring to a relatively greater number of copies of an allele or genotype passed on to future generations. In addition, ALL of the individual's alleles are passed on to each offspring, not just half of them. However, in the end, all of those offspring are clones (excepting any accumulated mutations). That means that any environmental change that would be detrimental (or fatal) for one of them, would likely harm all of them. This is the likely explanation for why very few species are exclusively asexual, while many are able to reproduce both sexually and asexually. Environments with constant conditions, as opposed to variable conditions, are more likely to permit the survival of species who primarily reproduce asexually

"Prokaryotes" reproduce:

asexually through binary fission, but they also have multiple mechanisms for horizontal gene transfer that increase genetic diversity.

Plant and fungi growth

Plants and fungi are each much more flexible in their growth than animals. They have indeterminate growth, meaning there is no set stopping point. Another, connected, difference in growth and body plan of plants compared to animals is that plants are modular. This term is used here similarly to how it is used by non-scientists. The plant body is made up of repeating units, and it can have many of those units or few. Plants are made up of shoots (the above-ground portion) and roots (the below-ground portion). For the shoots, the module for many plants is a segment of stem, a leaf, and a bud. This segment repeats over and over again to make the full plant body, or it only repeats a few times such as in that small plant pictured above. In addition to giving flexibility in how these often-immobile organisms deal with variable environments, this also lets them sacrifice parts of their bodies. Animals are generally not module organisms. But. Exceptions, there are always exceptions. Some animals (like tapeworms) do have repeating segments, although not all segments are identical. Some animals (like some sea stars and flatworms) can lose a large chunk of themselves and just regrow that portion.

Plant dispersal

Plants are generally immobile as adults, but they do usually have a mobile stage. Exactly which stage is able to relocate depends on the clade of plants. Non-seed plants typical disperse as spores, with short-distance dispersal of sperm through water. Seed plants (angiosperms and gymnosperms) typically disperse as seeds, and they disperse sperm in pollen.

If you have a fern sporophyte that is heterozygous for 50% of its genes, and its gametophytes can only self-fertilize, what percentage of heterozygous genes would you find in the next generation of sporophytes?

A gametophyte produces all of its gametes by mitosis, meaning that they are all genetic clones of each other. So, a selfing gametophyte would be bringing two of those genetically identical cells together by fertilization. That means that the resulting zygote would be 0% heterozygous. It does not matter what level of heterozygosity was found in the sporophyte!

Synapomorphy

A shared, derived characteristic. On a phylogeny, you would see this as a trait that evolved at the base of a clade. It is derived as in it is newly evolved at that point in the lineage. It is shared among the descendants from that node and so is one of the pieces of evidence demonstrating the relationship among those lineages.

A general fungal life cycle

Again, they have a haploid and diploid phase. Again, they have mitosis and meiosis playing the expected roles. A major difference is that fungi have subdivided fertilization into two steps: the merging of cytoplasm and the merging of nuclei do not occur at the same time. They also do not have sperm and egg; there are no males and females. The hyphae that make up a fungal mycelium are usually haploid. If two genetically distinct individuals are available for mating, specialized hyphae can form in each individual and those hyphae merge. This merging of cytoplasm is known as plasmogamy. However, the nuclei remain distinct, and so the merged hypha is heterokaryotic (with two different types of nuclei, symbolized as 1n + 1n). Exactly what those specialized hyphae look like varies in the different phyla of fungi. In many fungi, those heterokaryotic hyphae will continue to grow, forming a multicellular mushroom that is also heterokaryotic. In those species, it is only on the sporeforming surfaces of the mushroom that the next phase happens: karyogamy. This is when the two haploid nuclei finally merge, producing diploid nuclei. Fungi do not stay diploid for long, meiosis follows immediately, producing haploid spores that are dispersed.

A general plant or animal life cycle

All sexually reproducing plants and animals fit into the general scheme shown in this figure. There is a phase in the life cycle that is diploid (2n), and a phase that is haploid (1n). Haploid (1n) cells are produced from diploid (2n) cells by meiosis, and diploid cells are produced from haploid cells by fertilization. Meiosis and fertilization are transition points between the haploid and diploid phases in plants and animals. In plants or animals, eventually some of those haploid cells will differentiate into sperm and egg cells, although this does not happen immediately in plants. When a haploid sperm and a haploid egg cell merge by fertilization, the resulting zygote is again diploid. The zygote is a single cell that then divides by mitosis to form the multicellular diploid phase of either a plant or an animal. Remember that meiosis only comes into play with sexual reproduction. It cuts the number of chromosomes in half! Losing half of your chromosomes is a very big deal. However, with sexual reproduction, fertilization returns the cells to the original number of chromosomes and so the species is not really losing chromosomes - they are just getting remixed. As noted above, some species can reproduce asexually, and those asexual portions of their life cycles only use mitotic cellular divisions. Things get a little more complicated with plants. Meiosis does not directly produce gametes, instead it produces spores. Those spores grow (or germinate) by mitosis, cell enlargement, and cell specialization into another multicellular phase, known as the gametophyte. As indicated, the gametophyte does produce gametes. However, the gametophyte is already haploid, and so it produces gametes (again called egg and sperm) by mitosis. These egg and sperm merge by fertilization to produce a zygote, which grows by mitosis and cell specialization into an adult diploid plant. That phase of the plant life cycle is known as the sporophyte, or the "spore-producing plant." The sporophyte has a specialized structure (or structures) known as a sporangium (or sporangia), which is where meiosis takes place to form spores. Thus, unlike animals, plants have two multicellular phases of their life cycle. This alternation of multicellular generations is a synapomorphy of land plants. It evolved in the common ancestor of all plants and has been passed on to each of the major groups of plants, with modifications evolving along the way. Some plants spend most of their lives as haploid organisms, and some are primarily diploid.

Which kingdom is characterized by an apical meristem and which by apical growth?

Apical meristems are found in plants and apical growth is found in fungi. In Plants, cell division takes place within groups of totipotent cells known as meristems. Apical meristems are found at the tips of stems and roots. The zone of cell division is the meristem. A stem tip grows upward, building on the older cells. Farther from the meristem, the older cells have had time to grow larger. Even farther from the meristem, the cells are old enough to have specialized into different cell types, such as what is seen in the developing leaf. The cells in the center of the leaf are specializing into vascular tissue (the circulatory system equivalent in plants). In Fungi, a hypha elongates at its tip, making the entire strand longer and sometimes branching into new strands. The hyphae do not pack together to form a solid mass, except when they are forming a macroscopic fruiting body (mushroom). The loose arrangement within the mycelium allows fungi to digest and absorb more nutrients from their environment.

Which of the following is FALSE in regards to mitosis and meiosis? A. Mitosis produces two genetic clones from a single parent cell. B. Meiosis produces haploid cells from diploid cells. C. Mitosis only occurs as part of sexual reproduction or attempted sexual reproduction. D. Mitosis is one of the major mechanisms of growth in a multicellular organism. E. Meiosis is required to produce gametes, but it does not always directly result in gametes.

C is false. Mitosis does NOT only occur as part of sexual reproduction. Mitosis is just another name for basic cell division in eukaryotes. It is one of the main ways that multicellular organisms grow.

Which of the following is TRUE in relation to growth? A. All cells in a mature plant body are totipotent. B. Fungi are characterized by apical meristems and plants are characterized by apical growth. C. Individual plant cells can migrate (move themselves) to new locations within the organism during development. D. A totipotent cell can potentially develop into any cell type of an organism, which means that it can potentially develop into an entire individual.

D is correct. A totipotent cell can potentially develop into any of the cell types of an organism, which means that a totipotent cell can also potentially develop into an entire individual by the processes of cellular division, expansion, and differentiation.

The importance of fungi to humans

Decomposition and nutrient cycling Plant growth Biochemists Food Pathogens

Why is it important for members of a species to be able to disperse? Include a discussion of the fitness implications for individuals who disperse versus those who stay close to their parents.

Dispersal is very important for the fitness of an individual. If a plant just dropped all of its seeds directly downward, they would have little opportunity to capture sunlight; they would have little room in the soil in which to grow their roots. If an animal lived right next to all of its offspring, they would similarly eventually run low on resources. A lack of dispersal means much greater competition for resources between the parents and offspring. This negatively impacts the fitness of everyone involved! Dispersal provides opportunities to find new resources, new habitats, new places to succeed. Dispersal also allows individuals to escape from pathogens and parasites. Dense populations are easier targets than those in which the individuals are more widely dispersed. Our recent adventures with social distancing has shown that effect in action! Another effect of dispersal is that it provides more opportunities for individuals to mate with distantly related individuals. This helps reduce the amount of inbreeding, potentially raising the fitness of those individuals. Inbreeding tends to lower genetic diversity and can also reveal deleterious recessive traits.

Eukaryotes reproduce:

Eukaryotes that reproduce sexually use meiosis to allow their alleles to recombine and then to combine with alleles from another individual. Many eukaryotes also have mechanisms for asexual reproduction, including budding off a new individual, breaking off part of the body that can then grow into a new individual, or asexually producing spores. Other eukaryotes can take an intermediate path - where they have recombination into gametes, but one individual produces both male and female gametes that then self-fertilize (also called "selfing").

Fungal spore dispersal

Fungi disperse by spores. These spores are microscopic and able to travel great distances through air currents. The spore-producing structures vary in different fungi. Some species (like molds) asexually produce hyphae that release spores. They have many tiny spore-producing hyphae.

When in the plant life cycle does the ploidy switch from haploid to diploid?

Meiosis changes the ploidy from diploid to haploid and fertilization changes the ploidy from haploid to diploid. This is true for both plants and animals.

What process produces egg cells in mosses?

Meiosis produces spores, which grow by mitosis into gametophytes, which then produce egg cells and/or sperm cells by MITOSIS. This is true for all plants, not just mosses and is a major difference between plants and animals.

There are three ways a multicellular organism can grow:

Mitotic cell division (one cell becomes two identical cells), cell expansion (one cell becomes bigger), and cell differentiation (cells specialize into different types with different functions).

Specifically, why would higher genetic variation likely increase the success of a set of offspring?

Natural selection can only select among alleles that are available in a population. More genetic variation means more options and a greater likelihood that one of those individuals will be able to survive and reproduce.

Which kingdom is characterized by cells that can move during development?

Of these three kingdoms, only animals have individual cells that can move within the body during development. Plants and fungi have cell walls that hold a cell in place. Those cells might seem to (slowly) move because they can still elongate or divide to extend a stem or a hypha into a new area, but the individual cells of the organism are not migrating around within the plant or fungus body. In most animals, cells within the blastula move inward to form the gastrula stage (see Fig. 26.11). That first hole into the gastrula will become important when classifying phyla of animals and forms into one of the major openings into the adult animal (mouth or anus). To follow the development of animals a little farther: a developing embryo (except in sponges) will have two or three germ layers: the ectoderm, endoderm, and mesoderm. Each germ layer develops into specific sets of tissue types.

Meiosis

One cell produces four daughter cells that each have half as many chromosomes as the parent cell. A diploid (2n) cell will produce haploid (1n) cells by meiosis.

Mitosis

One cell produces two daughter cells that are genetically identical to the parent cell. This allows growth and repairs in a multicellular body, as well as asexual reproduction for some species.

How to increase genetic variation?

One thing that is consistent across all of life is that it is often beneficial to increase genetic variation. Sexual reproduction allows recombination of alleles and brings together two sets of chromosomes. This leads to greater heterozygosity within individuals and can lead to greater genetic variation in the population as a whole. The level of variation depends on the sources of those two sets of chromosomes. Individuals of some species can self, such as plant individuals that produce both sperm and eggs. Individuals of other species are forced to mate not only with different individuals, but with individuals that are not closely related. There is a continuum of possibilities, with high levels of inbreeding on one end, and high levels of outcrossing on the other. The difference is whether the mates are closely or distantly related.

Which of these distinguish animals from plants and fungi? That is, which of these is TRUE for animals and FALSE for plants and fungi? (Select ALL that apply.) A. The organism can enter into new parts of their habitat. B. All stages of the life cycle are mobile. C. The body can move using environmental forces. D. The adult body develops from a single cell known as a zygote. E. None of the above characterize animals but not plants or fungi.

Only E is correct. A is true for all. Many plants and fungi can enter new habitats by growing into them. Some individuals can also disperse into new habitats. B is false for all, there are examples of animals that are sessile (immobile) as adults, such as corals and sea squirts. C is true for many plants and fungi - dispersing by wind or water. D is true for animals and plants.

Comparison:

Remember that basically all eukaryotes are either photoautotrophs or chemoheterotrophs. Plants and "algae" are autotrophs. Animals, fungi, and "protozoa" are heterotrophs. Cell walls are convenient way to distinguish the three multicellular kingdoms: animals lack cell walls, plants have cell walls of cellulose (like those shown in the picture here), and fungi have cell walls of chitin. Chitin is also what makes insects crunch if you step on them (not that you would do that, I'm just saying).

Seed plant life cycle

Seed plants are heterosporous: they have spores of two sizes. Most other plants are homosporous: all of their spores are the same size. In seed plants, the smaller male spore develops into a male gametophyte and the larger female spore develops into a female gametophyte. Ovules hold a female spore, which develops into a female gametophyte, which produces an egg cell. • Pollen grains develop from male spores and grow into the male gametophyte, which delivers sperm to the egg cell. Pollen allows for pollination: the movement of pollen (and thus sperm) from the male portion of a plant to the female portion of a plant without the sperm needing to swim through an external environment.

Plant seed and fruit dispersal

Seed plants have packaged their sporophyte embryos, with a food source, inside a portable seed coat. These seeds have adapted for dispersal in many ways. Some have wings to aid in wind dispersal. Some have an edible portion, to encourage dispersal via an animal's digestive tract. Others force animals to disperse their seeds without providing a reward.

What are some of the ways that organisms are structured or behave that lead to more outcrossing rather than inbreeding?

Separation of the male and female gametes in time on one individual. An organism may be hermaphroditic, but still only produce one gamete at a time. Many flowering plants use this strategy. Separation of the male and female gametes in space on one individual. Some organisms produce both egg and sperm at the same time, but the gametes are positioned so that they do not come into contact. Again, many flowering plants have this strategy, including plants that position their stamens and carpels so that the part that releases pollen and the part that catches pollen do not touch. Earthworms do this as well - each individual is hermaphroditic, but they cannot self-fertilize. Separation into male and female individuals, with each only producing one type of gamete. Separation of more closely related individuals through dispersal of offspring. Genetic incompatibility such that gametes from closely related individuals cannot undergo fertilization.

In humans, sperm is _____.

Sperm are haploid (1n) and produced by meiosis in animals.

Animal dispersal

You know that animals can move. Dispersal of offspring can thus be straightforward: they can run, swim, slither, or fly away. These videos show how some animals that are sessile (immobile and fixed to one place) as adults are still able to disperse by having mobile gametes and larvae.

A general animal life cycle

The basic animal life cycle is hopefully familiar to you. We are animals, and so we have all personally experienced parts of the animal life cycle. The diploid phase of animals and plants is somewhat similar. There is a zygote, it grows by mitosis, cell enlargement, and cell specialization into a multicellular diploid adult, and that adult has specialized structures in which meiosis occurs. In animals, the gametes (egg and sperm) are formed directly from meiosis. They merge by fertilization to form that zygote, which in animals then develops into a blastula. Animals are different from plants and fungi in that their cells can move within the body as part of development. Very early in development, this movement includes the inward movement of some cells of the blastula to form the gastrula stage, as previously mentioned. There are many variations on this simple life cycle, but all sexual life cycles in animals follow this general scheme. A major difference between some groups of animals is whether fertilization is internal or external. Gametes require a wet environment to survive because they can easily lose water and because animal sperm swim to get to the egg. As a result, external fertilization only occurs in aquatic species. This relies partly on chance for the sperm and egg to meet. As a result, a large number of gametes must be release. Seed plants with wind pollination (wind delivery of pollen) have a similar problem, but in their case, they have protected their sperm within a pollen grain and so it can travel in the air. However, terrestrial animals largely rely on internal fertilization that takes place within the female body.