bioramblings

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The Biostation Recap - Final Species Counts!

For those of you that have been here a while, you may remember that I was going on an adventure at my college's biostation for a class, helping to identify critters we captured and getting an idea for the populations on the property. Here's the results of all that we found:

Lepomus macrochirus - Bluegill (141 total, 78 were marked for a mark-recapture study, once released, we caught 63 bluegill and recaptured 3 of the original 78)

Etheostoma exile - Iowa Darter (8)

Dragonfly larvae - 9

Umbra limi - Central Mudminnow (2)

Micropterus salmoides [juvenile] - Largemouth Bass (1)

Ambystoma maculatum - Spotted Salamander (1)

Carabidae family - Ground Beetles (4)

Libellulidae family - Skimmer Dragonfly (1)

Lithobates clamitans - Green Frog [tadpoles] (2)

Planorbella trivolvus - Marsh Ram's Horn [snail] (1)

Anaxyrus americanus - American Toad (14)

Lithobates clamitans - Green Frog [adults] (4)

Lycosidae family - Wolf Spider (1)

Lythobates sylvaticus - Wood Frog [adults] (17)

Microtus pennsylvanicus - Meadow Vole (2)

Cambarus species - Crayfish (7)

Plethodon cinereus - Redbacked Salamander (1)

Gastropoda class - Slug (3)

Peromyscus leucopus - White-footed Deer Mouse (5)

Lepomus gibbosus - Pumpkin Seed Sunfish (1)

Chrysemys picta - Painted Turtle (1)

Chelydra serpentina - American Snapping Turtle (5)

- Snapping turtles varied in length:

- 10.5"

- 14"

- 11"

- 13.5"

- 11"

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A Return!

Hey hi! It's been a while! I'm finishing up my senior year of college this semester and I've been quite busy with my senior thesis and research. Best thing is, I actually got a statistically significant result from my research! It's been a great run here and I'm very excited and proud of myself for the work that I've done!

I have some projects lined up for myself in the future once I graduate, including taking a virtual scientific illustration course to build my portfolio for graduate school and formatting all of my notes into easy to read, type formats for my future reference alongside my textbooks.

When I get back into the swing of things and start formatting my notes, I'll start the bioramblings "courses" up again with all the material I've gotten from my classes.

Hope y'all have been doing well, and my apologies for my prolonged absence!

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A Brief Update

Hey hi everyone, so sorry for the radio silence. My summer research project has been draining me more that I was expecting, to be completely honest. By the time I get home for the day all I want to do is rest lol

A new school year is starting soon, and I'll be frantically working on my portfolio for grad school. Maybe you'll get some sneak peeks, guess we'll see ;)

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Biostation, Days 4, 5, and 6 - 5/13 thru 5/15/21

More eventful times! I'll keep it short.

5/13

We went river rafting today! It was a great time. My arms were killing me through a good part of it but it was so much fun! The river was super chill and relaxing, but the water was frigid. We saw some cool wildlife too, including a muskrat, a duck, an osprey, and a bald eagle.

5/14

I went on a long-ass hike across the entire property. It took about 2 hours, including stops for water and pictures. I'm sore as hell now. Also helped to identify 23 bluegill fish.

5/15

Day off! Plan today is to just rest. I sketched one of our bluegill yesterday and I'm going to try to color it today. Identified 21 bluegill, 1 juvenile largemouth bass, and 1 male Iowa darter.

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Biostation, Days 2 and 3 - 5/11 thru 5/12/21

Hi friends, sorry for disappearing!! We've had an eventful two days up at the biostation.

Yesterday, we set our minnow traps and the trap net.

The minnow traps were quite interesting to set, as we had to put on chest waders and wade out into a swampy area of the lake to drop them in the water. The water was pretty cold and the mud and sediment at the bottom of the lake was really thick, making it super easy to get stuck in the lake. It wasn't too bad with the whole class out setting them though.

The trap net was a bit of a different story. There's a very specific way that it has to be set up, and it's not entirely easy, either. We went out in a couple boats to get the net set, and all in all it only took us about an hour and a half. My team got our section done on the first try, but we had some difficulties with the other sections due to high wind and unforgiving current. We eventually got it set, though, and it appears to be doing its job!

Nothing in the herp traps today, unfortunately, but the minnow traps we set did actually catch a few things! We currently have 2 juvenile bluegill, 1 Iowa darter, and a dragonfly larva in our fish tank. Hopefully we'll catch more interesting things tomorrow.

We also got a full tour of the property today! It gave me a nice rout to take for a hike, which I may take on Friday and get some shots of all the different biomes we have on the property. Hopefully I'll get some good wildlife shots, too!

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Biostation, Day 1 - 5/10/21

Today has been a bit of an adventure! We had class at 9 this morning (no sleeping in for me til the weekends), and that ran till noon, but then the fun stuff started!

We're doing some field work while we're up here, so today we set up the "herp" traps. These are thin sheets of flexible metal that are flushed to the ground that direct small critters like frogs, salamanders, mice, snakes, etc. towards buckets buried in the ground. We're going to start collecting our findings tomorrow, hopefully we'll see some cool things! I'll be sure to update when we do.

Along the same vein, we found a red-backed salamander today and I got to hold it! It was very small and cute and it tickled when it walked on my hand. No pictures, unfortunately, but it was a cute lil thing. We were supposed to set up fish traps today but that didn't happen unfortunately.

I went on a hike as well, but it unfortunately got cut short due to rain (I had my camera out with me and didn't want it getting wet).

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Evil biology facts that fill me with Fear :)

hey, I heard y’all like evil biology facts like knowledge about horse blood types.

well! today I was researching alternative biochemistries extraterrestrial life could use and. man. I think Earth life is fucked up enough for me thanks

biological dark matter. WHAT DO YOU MEAN MY BLOOD HAS DNA IN IT FROM NO KNOWN SOURCE. YOU CAN’T JUST SAY THAT COME BACK HERE

One specific cave that has been sealed for 5.5 million years and has developed an ecosystem completely dependent on chemosynthetic bacteria.

Was anybody going to tell me that bacteria have decided iron is yummy and are eating the Titanic, or was I supposed to just read that myself

Terrible Berry (yes, that’s what the genus name means). This whole thing is so fucked up. These scientists were testing whether radiation could be used to kill pathogens in food, so they dosed a tin of meat with enough radiation to kill any known living organism (as one does) but guess what, it still fucking spoiled because of THIS BASTARD FUCKER.

(seriously, why is it like this? WHY has a bacterium evolved to chill in radioactive waste like it’s a soothing Jacuzzi tub? What does it know that we don’t know?)

(ANSWERS. I WANT ANSWERS, YOU CHERNOBYL ASS BITCH.)

Cursed worm, which has no mouth or digestive system and depends entirely on five (5) different species of bacteria, which consume hydrogen sulfide, hydrogen monoxide, and carbon monoxide, for food. How do you, a worm, even...figure out how to do...all that?

Bone worms. At least they like their bones already dead. I still could have gone without knowing this was a thing.

“Oh, parasitic plant, that sounds c—WHAT THE FUCK IS THAT THING”

I am like half convinced this is made up. Seriously, bacteria grow their own electrical wires and we just let them?

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Genetics (6) - Sex Determination

The fundamental difference between males and females in multicellular organisms is the gametes they produce. Males produce sperm while females produce eggs. There are multiple chromosomal sex determination systems, which we will go over in this section.

First is the XX-XO system, in which the XX chromosomes encode a female and the XO chromosomes encode for a male. An example of this system is grasshoppers, and it is important to remember that the O here stands for a lack of a chromosome.

Next is the XX-XY system, in which XX encodes a female and XY encodes a male. This system is displayed in mammals, humans included. The ZZ-ZW system operates in a similar manner to the XX-XY system, but the genders encoded is reversed. In this system, ZZ encodes a male and ZW encodes a female. This system is see in birds, snakes, butterflies, some amphibians, and fish.

Finally, we have the haplodiploidy system seen in bees, wasps, and ants. In this system, the organism with a haploid set of genes are males, and those with diploid sets are females.

There are also genetic sex determining systems and environmental systems. In the genetic system, there are no sex chromosomes, only the sex determining genes. This system is found in some plants, fungi, protozoans, and some fish. In the environmental sex determining system, environmental factors are what determine the organism’s sex. Examples of this are the temperature at which turtle eggs develop and the position of a limpet within a limpet stack.

Many plants (and some animals) also exhibit hermaphroditism, which is the presence of both sexes in the same organism simultaneously. Many plants are hermaphrodites and are thus able to self-pollinate without the need of pollinators like bees.

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Plant Physiology (6) - Solute Transport

Plant cells are separated from their environment by a thin plasma membrane and a cell wall. They must facilitate and continuously regulate the inward and outward traffic of selected molecules and ions as the cell does the following: taking up nutrients, exporting wastes, regulating turgor pressure, and sending chemical signals to other cells.

There are two perspectives for membrane transport: the cellular level and the whole plant level. On the cellular level, the process of membrane transport contributes to cellular function and ion homeostasis. On the whole plant level, it contributes to water relations, mineral nutrition, and growth and development.

Solutes and ions moving into cells and between compartments within the plant requires the membrane to be crossed. The cellular membrane is composed of a phospholipid bilayer and proteins. The phospholipid in and of itself sets up the bilayer structure. Phospholipids have hydrophilic heads and fatty acid tails. The hydrophilic heads of the lipids face outwards towards the inter and extracellular solutions while the hydrophobic, fatty acid tails face inside the bilayer away from the inter and extracellular solutions. The plasma membrane is fluid, and the proteins in it move in a fluid lipid background.

Membrane potentials arise from charged solutes crossing the cellular membrane at different rates. This creates a driving force for ionic transport. Membrane potential is maintained by energy-dependent electrogenic pumps that move ions against the gradient. Electrogenic pumps are ATPases which are enzymes that split ATP. ATPases use ATP energy to “pump” out protons to create a charge gradient. H+ gradients create a type of “battery” to power transport. To prove that proton gradients power transport, all that needs to be done is adding cyanide to a plant. Cyanide rapidly poisons the mitochondria and depletes the cell’s ATP. Membrane potential levels fall to levels seen with just diffusion.

Membrane potential has 2 parts, diffusion and electrogenic ion transport, the latter of which requires energy.

Ion homeostasis occurs in plant cells. Plant cells segregate ions based on their function or role and their potential toxicity. This ion segregation creates a balance, which may require energy. Ion concentrations in the cytosol and vacuole are controlled by active and passive transport. The vacuole takes up 90% of plant volume and contains the bulk of cell solutes. The control of cytosol ion concentrations is important for regulations of enzyme activity. The cell wall is not a permeability barrier and is not a factor in solute transport.

Solute transport depends on gradients and electrochemical potential. Electrochemical potential has two parts: concentration and charge. These two parts together dictate the electrochemical potential for the membrane.

Passive transport is movement down the electrochemical gradient from areas of a more positive charge to a more negative charge. Active transport is movement against an electrochemical gradient from a more negative to a more positive. Solutes alone must follow the rules of the electrochemical potential and move passively. If this solute is not what a cell or tissue needs, two components are required somewhere to counteract its natural tendency: energy and membrane transport proteins.

Three types of membrane transporters enhance movement of solutes across plant cell membranes. First are channels, which are passive transporters. These are transmembrane proteins that work as selective pores. The size of the pore determines the specificity. These allow for movement down the gradient are nondirectional. This sometimes involves the binding of the solute to the channel. One such example is a gate, which open and close the pore in response to signals, such as light and hormone binding. Only potassium can diffuse either inward or outward.

Carriers are the second class of transport proteins. These do not have pores that extend completely through the membrane. Instead, the substance being transported is bound to a specific site on the carrier. Carrier proteins are specialized to carry specific organic compounds. The binding of the molecule causes the carrier t change shape. This exposes the molecule to the solution on the other side of the membrane. The transport is complete after the solute dissociates. This occurs at a moderate speed and is more specific than channels. It’s unidirectional and can be either active or passive. Binding to a carrier is very similar to enzyme binding site action.

In active transport, membrane transport must couple the uphill transport of a molecule with the energy releasing event. Primary active transport uses energy sources from the electron transport chain of the mitochondria or chloroplasts or the absorption of light by a membrane transporter.

Pumps provide movement against the gradient. They are unidirectional transporter ions and very slow. They have significant interaction with the solute and the process is expends energy.

Secondary active transport couples the uphill transport of molecules with the downhill transport of another. The initial conformation of the protein allows protons from outside to bind to the pump. The proton binding alters the shape of the protein to allow the second molecule to bind. The binding of the second molecule alters protein shape again and exposes both binding sites to the inside of the cell. The release of both these molecules restores the pump proteins to their original conformation. In symport, both substances move in the same direction. In antiport transportation, the substances move in opposite directions. This requires a proton gradient provided by electrogenic pumps.

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Genetics (5) - Dihybrid Crosses and Independent Assortment

Similar to a monohybrid cross, dihybrid crosses examine two inherited traits at a time. Dihybrid crosses operate on the principle of independent assortment, and they are most commonly a cross between two doubly heterozygous individuals.

This leads us to the topic of independent assortment. In a cross involving two or more traits, the principle of independent assortment states that the alleles for each trait separate individually. This only applies if the genes are not linked (on the same chromosome), as linked genes do not assort independently.

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Plant Physiology (5) - Stomatal Conductance and Plant Nutrition

Stomatal conductance describes the diffusion of gas through plant stomata. Plants regulate their stomatal aperture in response to environmental conditions. This is described either as a conductance or a resistance (conductance is reciprocal of resistance). Stomatal conductance can be a good indicator of plant water status, as many plants regulate their water loss through stomatal conductance.

Do the stomata control water loss, or is another factor at play? In still air, the boundary layer resistance of the leaves controls leaf water loss. In moving air, stomatal resistance is what controls the water loss in the leaves. Boundary layer conductance depends on wind speed, leaf size, and the gas being diffused across the stomata. Blue lights stimulate stomatal opening.

There are some anatomical contributions to a plant’s boundary layer resistance to water loss, including the leaf’s shape and thickness, surface area, presence or absence of trichomes (hairs), presence or absence of pits around the stomata, leaf orientation, and whether or not the leaf has a waxy surface.

The transpiration is the ratio of water los to carbon gain. A plant loses 400 water molecules per every carbon molecule. The reciprocal of this is water use efficiency. This depends on three factors: the gradient driving water loss is 50 times higher, carbon dioxide diffuses more slowly, and carbon dioxide has farther to diffuse in the cell.

Mineral nutrition is very important to the overall health of the plant. Keep in mind that plants are capable of making all their necessary compounds from inorganic compounds and elements in the environment. They are supplied with all the carbon, hydrogen, and oxygen they could ever need. In order to get the other elements they need, they must be obtained from the soil.

A mineral is an inorganic element that is acquired mostly in the form of inorganic ions form the soil. A nutrient is a substance that is needed to survive or is necessary for the synthesis of organic compounds. Plants require 9 macronutrients and at least 8 micronutrients, many of which are essential. An essential element is required for a plant to grow from a seed and complete its life cycle. There are 17 essential elements: nitrogen, carbon, phosphorous, copper, nickel, sodium, potassium, oxygen, manganese, molybdenum, hydrogen, calcium, iron, boron, sulfur, magnesium, zinc, and chlorine.

An element that is essential is universal for all plants. Its absence would prevent the completion of the life cycle and would lead to deficiency. An essential element is required for some aspect of mineral nutrition. A beneficial element is often limited to only a few species. These elements stimulate growth and development, and may be required in some species of plant.

There are four basic groups of mineral elements. Group one is composed of nitrogen and sulfur, and they form organic components of plants. These are assimilated via biochemical reactions involving redox reactions. Group two elements are phosphorous, silicon, and boron. These are used in energy storage reactions or maintaining structural integrity. These elements are present in plant tissues as phosphate, borate, and sulfate esters. Group three elements - potassium, calcium, manganese, chlorine, magnesium, and sodium - are present in tissues as ions or ions bound to substrates. These are particularly important in certain roles, such as enzyme cofactors and regulation of osmotic potentials. Group four elements are the rest of the essential nutrients, and these play important roles in reactions involving electron transport. Some are also involved in the formation and regulation of growth hormones and the light reactions of photosynthesis.

Nutrient deficiencies occur when concentration of nutrient decreases below the typical range. Deficiencies of certain nutrients lead t specific visual, often characteristic symptoms reflective of the role of that nutrient in the plant. A nitrogen deficiency will result in the yellowing of mature, lower leaves. Potassium deficiency will lead to leaf margin necrosis. Calcium deficiency will lead to blossom-end rot, in which case the plant will flower and produce fruit, but severe necrosis occurs on the fruit. In cases of magnesium deficiency, interveinal chlorosis occurs on the plant, and in iron deficiency the plant experiences generalized chlorosis.

The location of deficiency symptoms reflects the mobility of the nutrient. Nutrients are redistributed in the phloem. If deficiency is appearing in old leaves, the nutrient is mobile and has been directed to the newer leaves. If deficiency is appearing in new leaves, the deficiency is in a nonmobile nutrient.

The soil also affects nutrient absorption. The pH of the soil affects the growth of plant roots and soil microbes. Root growth favors a pH of 5.5 to 6.5. Acidic soil conditions weathers rocks and releases potassium, magnesium, calcium, and manganese. Decomposition lowers soil’s pH. Rainfall leaches ions through the soil, which forms alkaline conditions, and negatively charged soil “holds on” to nutrients that are then released through cation exchange.

Mycorrhizal associations can be beneficial for plant nutrition, as mycorrhizal fungi can increase the surface area of the roots and provide nutrients to the plants in exchange for carbon.

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Genetics (4) - The Principle of Segregation, Dominance, and Test Crosses

Last time, we covered the introduction to Mendel’s experiments in heredity. Today, we’re going to talk about Mendel’s first law, the concept of dominance, and the test cross.

Mendel’s first law, also known as the principle of segregation, states that each individual diploid organism possesses two alleles for any particular characteristic. The two alleles segregate when gametes are formed, with one allele going into each gamete.

This basic principle now leads us into the concept of dominance. When two different alleles are present in a genotype, only one appears in that trait’s phenotype. The trait that appears is the dominant allele.

What about heterozygotes, though? Since they possess both the dominant and recessive alleles, how can we tell a heterozygote from a dominant homozygote? This can be done using a test cross, which is a cross between an unknown genotype and a homozygous recessive genotype. Let’s use Mendel’s pea plants for an example. In pea plants, a tall plant could be encoded by the alleles Tt or TT. To determine its genotype, we cross the unknown plant with a homozygous recessive short plant (tt). If the unknown plant was homozygous (TT), all the progeny from that cross would be tall plants. If the unknown plant was heterozygous (Tt), half the progeny would be tall and the other half would be short.

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Plant Physiology (4) - The Xylem

The xylem is the main water conducting tissue of vascular plants. The xylem tissues arise from individual cylindrical cells that are oriented end to end. At maturity, the end walls of these cells dissolve, and their cytoplasmic contents die. The result of this internal death is the xylem vessel, a continuous, nonliving duct that carries water and some dissolved solutes, such as inorganic ions, up the plant.

Water moves up the xylem through a system called “bulk flow.” This sort of flow comes from three main mechanisms of movement. First is transpirational pull which occurs due to water’s properties of cohesion and adhesion. When water is evaporated from the leaves through the stomata, cohesion between water molecules pulls more molecules into the leaves to take their place. This results in water flowing up through the plant’s xylem against gravity. Water potential also plays a part in bulk flow, as water potential is highest in the soil and lowest in the leaves. Water moves from an area of high concentration to an area of low concentration, thus moving up the plant. Finally, root pressure results in the upward push of xylem sap due to the flow of water from the soil into the root cells.

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Genetics (3) - Mendel and the Basics of Heredity

Gregor Mendel was a friar that lived during the 1800s. Known best for his work with pea plants, Mendel was also a meteorologist and a mathematician. Today, however, we are going to focus on his success in genetics. Mendel used an experimental approach to studying heredity, and he studied easily differentiated characteristics. In order to analyze his results, he used mathematics. Mendel’s work formed the basis of our understanding of genetics.

Before we go any further, we should define some important genetic terms.

A gene is an inherited factor encoded in DNA that helps determine a characteristic.

An allele is one of two or more alternative forms of a gene.

A locus is a specific place on a chromosome occupied by an allele.

A heterozygote is an individual organism possessing two different alleles at a locus.

A homozygote is an individual organism possessing two of the same alleles at a locus.

A genotype is the set of alleles possessed by an individual organism.

A phenotype is the appearance or manifestation of a characteristic.

Now that we have gotten these terms out of the way, let’s talk about genetic principles. Genetic principles account for the passing of traits from parents to offspring. There are two different hypotheses about genetic inheritance. The first of these, the blending hypothesis is the idea that genetic material from the two parents blends together to create the characteristics of their offspring. Second, the particulate hypothesis is the idea that parents pass on discrete, heritable units, known as genes.

To test his theories about inheritance, Mendel used genetic crosses. The first of these, the monohybrid cross, is a cross between two parents that differ in a single characteristic. This cross leads us to four conclusions:

1. One characteristic is encoded by two genetic factors.

2. Two genetic factors (alleles) separate when gametes are formed.

3. The concept of dominant and recessive traits.

4. Two alleles separate with equal probability into the gametes.

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Plant Physiology (3) - Osmosis and Water Potential

Osmosis is the passive diffusion of water. The rate of this process responds to several different things, such as differences in permeability, solute concentrations, and pressure.

Water potential, symbolized Ψ, is the chemical potential of water. It is the difference in energy between a substance in a given state and a standard state, and it is based on free energy, which is the capacity to do work. Water potential is influenced by concentration, pressure, and gravity, which is demonstrated in the equation below:

Ψ = Ψs + Ψp + Ψg

In the equation above, Ψ = water potential, Ψs = osmotic potential, Ψp = pressure, and Ψg = gravity, a measurement that is ignored for plants of 5 meters in height and below.

Now let’s take a look at osmotic potential (Ψs). Osmotic potential gives the effects of solutes on water. Osmotic potential can be reduced by diluting water, and it operates independent of the nature of the solute. In ideal conditions, osmotic potential can be calculated using the following equation:

Ψs = -RTCs

wherein -R = 8.32 J mol-1 K-1 (gas constant) and Cs equals the concentration of solutes in moles. The osmolarity of a solution is the concentration of dissolved solids.

Next, let’s move on to pressure potential (Ψp). Pressure potential is the hydrostatic pressure in excess of ambient atmospheric pressure. If the pressure is positive, in plants, that is equal to turgor pressure. If negative, the pressure is tension.

How can we measure water potential? For plants, we can measure the water potential in situ (within the plant cell) using a tool called a psychrometer. Pressure chambers can also be used, as can the matric potential (Ψm). Matric potential is the sum of the osmotic and pressure potentials, and it is used when there is very little water around. This method is often used with seeds or arid soils.

Water potential in plants is usually 0 mega Pascals (MPa) or less. We will only see movement against the water potential gradient if water movement is coupled with some solute. The typical water potentials in well-watered herbs ranges from -0.2 to -0.1 MPa, and in well-watered woody plants it sits around -2.5 MPa. If the area is arid, the water potential can be as low as -10 MPa. Pressure potentials within cells tends to range from 1 MPa to 3 MPa.

In plant cells, a change in water potential is accompanied by changes in pressure with little volume change. Turgor pressure will approach zero with a cell volume decrease of 10-15%, and this is completely dependent on cell wall elasticity. Stiffer cell walls have bigger changes. As water moves across a membrane or down a gradient, the rate of diffusion slows down. In plant physiology, the measurement of “half-time” is the time it takes to decrease the rate of flow by half.

Plants are seldom fully “hydrated,” as transpiration doesn’t allow it. Plants are constantly moving and losing water on a day in, day out basis. This makes water potential an important factor in plant physiology.

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Genetics (2) - Cell Reproduction

Cell reproduction is an important part of life. Without it, we would not exist or even grow. There are two main types of cells, each of which replicate in a similar but different manner.

In prokaryotes, cell division is a simple process. It is a simple division that results in the separation of replicated circular chromosome. There is a single origin of replication, and prokaryotes have very high rate of replication. Eukaryotes replicate differently, and their process of division is more complicated. Eukaryotic genetic information is stored in chromosomes, which are grouped in homologous pairs.

Because of their general structure, eukaryotic cells have different varieties based on the amount of genetic information they carry. A haploid cell carries one copy of each chromosome, while a diploid cell carries two copies.

Eukaryotes reproduce through a process known as the cell cycle. This process leads up to mitosis, which is the main process of cellular division. The first step in the cell cycle is interphase, an extended period between cell divisions during which chromosomes replicate. Interphase can be grouped into three additional phases: G1, S, and G2.

During the G1 phase, cells are growing normally, and all the proteins they need for division are synthesized. After the G1 phase, cells enter the S phase once they pass the G1/S checkpoint, a regulated decision point that determines whether or not a cell is ready to proceed through the cell cycle. In the S phase, DNA is synthesized and replicated, after which the cell phases into G2, where the biochemical preparation for cell division occurs. Here, the cell must pass the G2/M checkpoint before it can proceed into the mitotic phase. This checkpoint can only be passed if the DNA within the cell is completely replicated and undamaged.

The mitotic phase is when the cells properly replicate and split into two. There are four phases of mitosis. The first is prophase, in which the nuclear envelope disintegrates, the centrosomes double, and the chromatin condenses. The chromosomes then line up along the metaphase plate during metaphase, and the sister chromatids separate in anaphase. In telophase, the separated chromatids are isolated on opposite poles of the dividing cell, and the nuclear envelope reforms around them. Telophase is quickly followed by cytokinesis, the splitting of the cytoplasm and plasma membrane. This process produces two identical daughter cells.

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Plant Physiology (2) - Water and the Plant

Water is a compound that is crucial for all life, especially plants. For each gram of organic matter produced by the plant, 500g of water is run through the plant. Over its lifetime, a single plant loses over ten times its wet mass in water.

Water is crucial in the plant cell as it is what provides an important force known as turgor pressure. Turgor pressure is the internal hydrostatic pressure in a cell. This is important for cell enlargement, leaf expansion, gas exchange, phloem transport, membrane transport, and rigidity and mechanical stability. Turgor pressure is a physiological process that is easily witnessed in plants, as droopy leaves demonstrate an absence of turgor pressure. The cellulose cell wall is what allows turgor pressure to build up within the plant cell.

Let’s take a closer look at water and the plant cell. The cytoplasm within a cell is typically 5-10% of the cell’s total volume, and the amount of water within plant tissues changes depending on the type of plant. In vegetables, there is about 80-95% of the plant’s water within the tissues.

Woody plants like trees are mostly xylem tissue and have a much lower water percentage. Many plant cells in woody plants are dead. There are two types of wood in woody plants: sap wood, which is living, active xylem in the outer layers, and heart wood, the central wood of a plant that is hollow, dead xylem.

Seeds are an entirely different story. Seeds only have about 5-15% water content, and they are some of the driest plant tissue to be found. This helps the seed to survive in dormancy for extended periods of time. Since seeds have slower metabolisms, they don’t need as much water within their tissues, and their dryness makes it easier for them to absorb water from the environment when needed. The low water content of seeds also makes them less susceptible to fungal pathogens. Seeds must absorb large quantities of water to be able to germinate, a process known as imbibition.

Now let’s look at water on the whole plant level. Plants must constantly move water through their bodies. Because of the stomata, a plant is constantly exposing its interior environment to the exterior world, causing it to constantly lose water. This is known as transpiration, and it’s the evaporation of water from leaves due to gas exchange and evaporative cooling. On a warm, sunny day, a leaf turns over 100% of its water content every hour. This process is necessary to keep water and minerals moving up from the roots. Water is most abundant in plants, but it is also the most limiting resource when it comes to plant productivity.

Now that we have examined water on the whole plant level, we can start looking at the properties of water itself. Water is made up of one oxygen atom covalently bonded to two hydrogen atoms. The oxygen atom is highly electronegative, making the water molecule polar. There is a partial negative charge on the oxygen and a partial positive charge on the hydrogens. Polarity is the key to water’s usefulness to life and to plants themselves.

Water is a universal solvent. It is good at dissolving different types of stuff, as it can dissolve polar, nonpolar, and ionic bonds. This is especially useful to plants and cells as many biochemical reactions happen within the cytosol of the cell, which is mostly made up of water.

The thermal properties of water also make it unique. Water has a high specific heat, which is the amount of energy required to raise the temperature of a compound. Water also has a high latent heat of vaporization, which is the temperature required to move liquid state molecules to a gaseous state. These thermal properties of water provide a buffer against sudden changes in heat. Plant and animal bodies require stability, and high temperatures denature proteins and enzymes necessary for life functions. If water didn’t have such thermal properties, the water in plant and animal bodies would change temperature so rapidly and violently that life would not be possible.

Water has other properties that make it important to life, especially to plants. Water is “sticky,” meaning it holds together well with itself and with other things. One example of this is surface tension, which is why water forms droplets. Liquid water molecules are much more attracted to themselves than the surrounding air molecules. Water molecules also exhibit high levels of cohesion (sticking to each other) and adhesion (sticking to other solid things like cell walls and glassware). Both of these properties, cohesion and adhesion, contribute to capillary action, which is when water climbs up and moves through a tube or surface. It also contributes to the tensile strength of water, which is the maximum force per area hat a continuous stream of water can withstand without breaking. Gas bubbles, however, reduce capillary and tensile strength. As bubbles expand in the absence of pressure, they can disrupt the flow of water and the tube itself. In plants, this creates a phenomenon known as cavitation, and it can be very destructive to the plant.

Water gets into cells through the plasma membrane via diffusion and osmosis. Aquaporins are channels in the plasma membrane that are water-selective. We will discuss diffusion and osmosis further in the next section.