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5.3: Pre-lab Questions - Biology

5.3: Pre-lab Questions - Biology


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5.3: Pre-lab Questions

Scientific Revolutions

The topic of scientific revolutions has been philosophically important since Thomas Kuhn&rsquos account in The Structure of Scientific Revolutions (1962, 1970). Kuhn&rsquos death in 1996 and the fiftieth anniversary of Structure in 2012 have renewed attention to the issues raised by his work. It is controversial whether or not there have been any revolutions in the strictly Kuhnian sense. It is also controversial what exactly a Kuhnian revolution is, or would be. Although talk of revolution is often exaggerated, most analysts agree that there have been transformative scientific developments of various kinds, whether Kuhnian or not. However, there is considerable disagreement about their import. The existence and nature of scientific revolutions is a topic that raises a host of fundamental questions about the sciences and how to interpret them, a topic that intersects most of the major issues that have concerned philosophers of science and their colleagues in neighboring science and technology studies disciplines. Even if the so-called Scientific Revolution from Copernicus to Newton fits the attractive, Enlightenment picture of the transition from feudalism to modernity (a claim that is also contested), the putative revolutions in mature sciences (e.g., relativity and quantum mechanics) challenge this Enlightenment vision of permanent rational and methodological standards underlying objective sciences and technologies that lead society along the path of progress toward the truth about the world. Today&rsquos scientific realists are the most visible heirs of this picture. Although many philosophers and philosophically or historically reflective scientists had commented on the dramatic developments in twentieth-century physics, it was not until Kuhn that such developments seemed so epistemologically and ontologically damaging as to seriously challenge traditional conceptions of science&mdashand hence our understanding of knowledge acquisition generally. Why it was Kuhn&rsquos work and its timing that made the major difference are themselves interesting questions for investigation, given that others (e.g., Wittgenstein, Fleck, Bachelard, Polanyi, Toulmin, and Hanson) had already broached important &ldquoKuhnian&rdquo themes.

Was there a Scientific Revolution that replaced pre-scientific thinking about nature and society and thus marked the transition to modernity? Which later developments, if any, are truly revolutionary? Are attributions of revolution usually a sign of insufficient historiographical understanding? In any case, how are such episodes to be explained historically and epistemologically? Are they contingent, that is, historical accidents and thus perhaps avoidable or are they somehow necessary to a &ldquoprogressive&rdquo science? And, if so, why? Is there an overall pattern of scientific development? If so, is it basically one of creative displacement, as Kuhn claimed? Do all revolutions have the same structure and function, or are there diverse forms of rupture, discontinuity, or rapid change in science? Do they represent great leaps forward or, on the contrary, does their existence undercut the claim that science progresses? Does the existence of revolutions in mature sciences support a postmodern or &ldquopost-critical&rdquo (Polanyi) rather than a modern, neo-Enlightenment conception of science in relation to other human enterprises? Does their existence support a strongly constructionist versus a realist conception of scientific knowledge claims? Are revolutions an exercise in rationality or are they so excessive as to be labeled irrational? Do they invite epistemological relativism? What are the implications of revolution for science policy? This entry will survey some but not all of these issues.


Culture Many ‘90s kids owned a Tamagotchi — or several. A new version of the digital toy arrives this summer as a resurgence in popularity attracts new generations of eager "Tama-parents." Travel Many ‘90s kids owned a Tamagotchi — or several. A new version of the digital toy arrives this summer as a resurgence in popularity attracts new generations of eager "Tama-parents."

5.3: Pre-lab Questions - Biology

The nucleus is a highly specialized organelle that serves as the information processing and administrative center of the cell. This organelle has two major functions: it stores the cell's hereditary material, or DNA, and it coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division).

Only the cells of advanced organisms, known as eukaryotes , have a nucleus. Generally there is only one nucleus per cell, but there are exceptions, such as the cells of slime molds and the Siphonales group of algae. Simpler one-celled organisms ( prokaryotes ), like the bacteria and cyanobacteria, don't have a nucleus. In these organisms, all of the cell's information and administrative functions are dispersed throughout the cytoplasm.

The spherical nucleus typically occupies about 10 percent of a eukaryotic cell's volume, making it one of the cell's most prominent features. A double-layered membrane, the nuclear envelope, separates the contents of the nucleus from the cellular cytoplasm. The envelope is riddled with holes called nuclear pores that allow specific types and sizes of molecules to pass back and forth between the nucleus and the cytoplasm. It is also attached to a network of tubules and sacs, called the endoplasmic reticulum, where protein synthesis occurs, and is usually studded with ribosomes (see Figure 1).

The semifluid matrix found inside the nucleus is called nucleoplasm. Within the nucleoplasm, most of the nuclear material consists of chromatin, the less condensed form of the cell's DNA that organizes to form chromosomes during mitosis or cell division. The nucleus also contains one or more nucleoli, organelles that synthesize protein-producing macromolecular assemblies called ribosomes, and a variety of other smaller components, such as Cajal bodies, GEMS (Gemini of coiled bodies), and interchromatin granule clusters.

Chromatin and Chromosomes - Packed inside the nucleus of every human cell is nearly 6 feet of DNA, which is divided into 46 individual molecules, one for each chromosome and each about 1.5 inches long. Packing all this material into a microscopic cell nucleus is an extraordinary feat of packaging. For DNA to function, it can't be crammed into the nucleus like a ball of string. Instead, it is combined with proteins and organized into a precise, compact structure, a dense string-like fiber called chromatin.

The Nucleolus - The nucleolus is a membrane-less organelle within the nucleus that manufactures ribosomes, the cell's protein-producing structures. Through the microscope, the nucleolus looks like a large dark spot within the nucleus. A nucleus may contain up to four nucleoli, but within each species the number of nucleoli is fixed. After a cell divides, a nucleolus is formed when chromosomes are brought together into nucleolar organizing regions. During cell division, the nucleolus disappears. Some studies suggest that the nucleolus may be involved with cellular aging and, therefore, may affect the senescence of an organism.

The Nuclear Envelope - The nuclear envelope is a double-layered membrane that encloses the contents of the nucleus during most of the cell's lifecycle. The space between the layers is called the perinuclear space and appears to connect with the rough endoplasmic reticulum. The envelope is perforated with tiny holes called nuclear pores. These pores regulate the passage of molecules between the nucleus and cytoplasm, permitting some to pass through the membrane, but not others. The inner surface has a protein lining called the nuclear lamina, which binds to chromatin and other nuclear components. During mitosis, or cell division, the nuclear envelope disintegrates, but reforms as the two cells complete their formation and the chromatin begins to unravel and disperse.

Nuclear Pores - The nuclear envelope is perforated with holes called nuclear pores. These pores regulate the passage of molecules between the nucleus and cytoplasm, permitting some to pass through the membrane, but not others. Building blocks for building DNA and RNA are allowed into the nucleus as well as molecules that provide the energy for constructing genetic material.


How to solve Aptitude Ratio and Proportion problems?

You can easily solve all kind of Aptitude questions based on Ratio and Proportion by practicing the objective type exercises given below, also get shortcut methods to solve Aptitude Ratio and Proportion problems.

Exercise :: Ratio and Proportion - General Questions

A and B together have Rs. 1210. If of A's amount is equal to of B's amount, how much amount does B have?

B's share = Rs. 1210 x 2 = Rs. 484.
5

Two numbers are respectively 20% and 50% more than a third number. The ratio of the two numbers is:

Let the third number be x.

Then, first number = 120% of x = 120x = 6x
100 5

Second number = 150% of x = 150x = 3x
100 2

Ratio of first two numbers = 6x : 3x = 12x : 15x = 4 : 5.
5 2

A sum of money is to be distributed among A, B, C, D in the proportion of 5 : 2 : 4 : 3. If C gets Rs. 1000 more than D, what is B's share?

Let the shares of A, B, C and D be Rs. 5x, Rs. 2x, Rs. 4x and Rs. 3x respectively.

Then, 4x - 3x = 1000

B's share = Rs. 2x = Rs. (2 x 1000) = Rs. 2000.

Seats for Mathematics, Physics and Biology in a school are in the ratio 5 : 7 : 8. There is a proposal to increase these seats by 40%, 50% and 75% respectively. What will be the ratio of increased seats?

Originally, let the number of seats for Mathematics, Physics and Biology be 5x, 7x and 8x respectively.

Number of increased seats are (140% of 5x), (150% of 7x) and (175% of 8x).

140 x 5x , 150 x 7x and 175 x 8x
100 100 100

7x, 21x and 14x.
2

The required ratio = 7x : 21x : 14x
2

14x : 21x : 28x

In a mixture 60 litres, the ratio of milk and water 2 : 1. If this ratio is to be 1 : 2, then the quantity of water to be further added is:


Try It Yourself!

Try this neat experiment to see what happens when bones lose their strength or flexibility. First, you'll need some bones. Chicken leg bones will work best. You can get these from a grocery store or restaurant after a chicken dinner.

Bending Bones

Step 1: Get two dry, clean bones of about the same shape and size. Make sure you've removed all the meat from around these bones.

Step 2: With the help of an adult, put one of the bones in a jar or bowl filled with vinegar. Make sure the entire bone is completely covered with vinegar. Put a lid or layer of plastic wrap over it to keep the vinegar smell from getting out. Wrap the second bone in plastic wrap and place it next to the jar.

Step 3: After three days, remove the first bone from the jar and rinse it off with water.

Step 4: Try to bend the bone that wasn't soaked in vinegar. What happens? How does it feel? Next, try to bend the bone that you soaked in vinegar. How does it feel compared to the first bone? Does it bend easily? What happens when you try to break it in half?

What happened? Vinegar is a mild acid. Soaking the bone in vinegar removes the calcium, which makes it soft and bendable.

Brittle Bones

Step 1: Get two dry, clean bones of about the same shape and size. Make sure you've removed all the meat from around these bones.

Step 2: With the help of an adult, put one of the bones in a baking pan and bake it in the oven at 250 degrees F for three hours.

Step 3: Remove the pan from the oven and let the bone cool down for a bit (at least 15 minutes) until you can touch it without burning yourself.

Step 4: Try to bend the bone that wasn't baked. What happens? How does it feel? Next, try to bend the bone that you baked. How does it feel compared to the first bone? Does it bend easily? What happens when you try to break it in half?

What happened? Baking the bone breaks down collagen. Without collagen, the bone is brittle and easy to break. If the bones in your body lacked collagen, they would break easily.


Watch the video: 1ο Θέμα Επανάληψης Βιολογίας Γ Γυμνασίου 1ο Κεφάλαιο (June 2022).


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