Because of biological multiplication, toxic substances present a larger threat to top predators than to primary consumers in the environment.
How does biomagnification work?
The buildup of a certain substance in the bodies of creatures at various trophic levels of a food chain serves as an example. The drug or chemical might not break down, accumulating in higher trophic levels as a result.
These dangerous substances pose a bigger threat to the ecosystem. Because the top predator feeds directly on the primary consumers, the poisonous component poses a higher problem to top-level predators than to primary consumers. These harmful components get gathered throughout their tissue.
To learn more about biomagnification here:-
https://brainly.com/question/7631542?referrer=searchResults
#SPJ4
.
How is the lunar-linked rhythm of fiddler crab courtship similar in mechanism and function to the seasonal timing of plant flowering? (See Concept 39.3.)
In both cases, the detection of periodic variation in the environment results in a reproductive cycle timed to environmental conditions that optimize the opportunity for success.
What is lunar-linked rhythm ?Seashore plants and animals are subjected to a rhythmic change by the lunar tidal rhythm, which is the regular ebb and flow of oceans and very large inland bodies of water. Typically, two high and two low tides occur each day (about 24.8 hours).
Circadian rhythms provide a crucial function by preparing your body for impending environmental changes including, for instance, the best times to be active, sleep, and eat. The sun's light/dark cycle is the most powerful external stimulus.Learn more about Circadian rhythm here:
https://brainly.com/question/10249604
#SPJ4
Three-chambered hearts with incomplete septa were once viewed as being less adapted to circulatory function than mammalian hearts. What advantage of such hearts did this viewpoint overlook?
Because some oxygen-depleted blood from the systematic circuit that was returned to the right ventricle would have mixed with the oxygen-rich blood in the left ventricle, the O2 level would be unusually low.
Why do certain animals' hearts have three chambers?Amphibians and reptiles have three chambers in their hearts for the following reasons: Their lower metabolic rates result in a lower oxygen need per litre of blood. A frog's heart, for example, contains three chambers: one ventricle and two atria.
What are the advantages of a three-chamber heart?A three-chambered heart is preferable to a two-chambered heart because it can exert greater pressure on the blood arteries to guarantee that oxygenated blood flows into the body and deoxygenated blood is sent to the lungs.
learn more about Three-chambered hearts refer
https://brainly.com/question/22715620
#SPJ4
In which two ways do cells use the sugar made in photosynthesis?
A. To produce more oxygen
B. To store chemical energy
C. To make more complex carbohydrates
D. To store inorganic matter
The two ways cells use the sugar made in photosynthesis are to store chemical energy and to make more complex carbohydrates. Therefore, options B and C are correct.
Glucose produced during photosynthesis is stored as chemical energy in the form of complex molecules like starch or glycogen. These energy-rich molecules act as long-term energy reserves that can be later broken down through cellular respiration to provide ATP.
It is also used as a building block to synthesize more complex carbohydrates like cellulose, which forms the structural component of cell walls in plants.
Learn more about photosynthesis, here:
https://brainly.com/question/34149583
#SPJ4
The cells that rhythmically and spontaneously generate action potentials in the heart are called ___
The cells that rhythmically and spontaneously generate action potentials in the heart are called pacemaker cells
The pacemaker cells are the ones that help in the maintenance of the action potential and that action potential work as an electrical clock that provides the automaticity to coordinate the pacemaker cells it divides the action potential into 4 phases among which in phase 4 the ion channels open that conducts slow, inward ( depolarizing Na+ ) currents and they are called as funny currents which cause the membrane potential to spontaneously depolarize, thereby initiating phase 4 and at the -50mV T type Ca 2 + channels open and further depolarize the cells and in some way, L type Ca+ channel opens when membrane reaches -40mV and this further results in the more Ca+ enter to depolarize the cell further until an action potential threshold is reached.
At phase 0 depolarization is primarily caused by increased Ca+ current through L-type channels that began to open toward the end of phase 4.. In contrast, the T-type channel's Ca+ current slows as these channels close and in phase 3 K+ channels open thereby increasing the outward directed hyperpolarizing K+ winds and decreases the inward of Ca+ and hyperpolarization takes place and then again enter in phase 4 hence the pacemaker cells maintain the action potential by dividing and circulating in 3 different phases.
To know more about pacemaker cells click at https://brainly.com/question/13956328
#SPJ4
After a cow is given antibiotics to treat an infection, a vet gives the animal a drink of "gut culture" containing various prokaryotes. Why is this necessary?
The prokaryotes in the cow's intestines that break down cellulose would most likely be killed by antibiotic therapy.
This is further explained below.
What is an Antibiotic?Generally, Antibiotics are drugs used to treat bacterial illnesses in both people and animals.
They do this by either killing the germs or by making it harder for them to develop and reproduce. Germs are bacteria.
They are everywhere in our bodies, both inside and outside, and in the surroundings.
In conclusion, The cellulose-digesting prokaryotes in the cow's intestines would probably be killed by antibiotic therapy.
Read more about Antibiotic
https://brainly.com/question/10868637
#SPJ1
Which is an abiotic factor? a a polar bear on an ice floe b a forest of deciduous trees c fungi and moss on a rotting log d an ocean current of cold water
The abiotic factor is (d) an ocean current of cold water.
Abiotic factor are those that do not perform the basic processes of life. These processes are: respiration, excretion, digestion, movement and reproduction. Although these factors do not perform any life processes, yet they are essential for the environment and the living organisms to sustain. The examples are: water, sunlight, soil, rocks, etc.
Ocean currents are the movement of ocean water. This movement is regulated by several factors like gravity, direction of wind, density of water, climate, etc. The ocean water can have movement in two directions: vertical and horizontal.
To know more about abiotic factor, here
brainly.com/question/1543548
#SPJ4
paleolithic cooking vessels such as the jomon vessel were decorated by pressing slender ribs of onto the body of the pot in a diamond pattern?
Jomon ceramic vases are the oldest in the world and their printed decoration, reminiscent of a rope, is the origin of the word jomon, which means 'cord pattern'. not diamond pattern.
What is Jomon ceramic vases?Most Jomon pottery has rounded bases and the vases are typically small. This shows that the pots would typically be used for cooking food, perhaps suitable for a campfire. Later pieces of Jomon pottery are more elaborate, especially during the Middle Jomon period, where the edges of pots became much more intricate and decorated.
With this information, we can conclude that The name Jomon itself means “standard rope”. This refers to the impressions on the ceramic surface that were created by pressing strings into the clay before it was heated to approximately 600-900 degrees Celsius.
Learn more about Jomon in brainly.com/question/2065011
#SPJ1
How does air in the lungs differ from the fresh air that enters the body during inspiration?
During inspiration, the diaphragm and external intercostal muscles flex, causing the rib cage to enlarge and move outward as well as the thoracic cavity and lung volume. Because the internal pressure is lower than the ambient pressure, air is drawn into the lungs.
Where on the body is the thoracic region?The thoracic spine is present in the upper and middle part of the back. Twelve vertebrae, designated T-1 through T-12, make up the thoracic spine. T-1 through T-5 nerves have an impact on the mid-back, abdominal, and upper chest muscles. The spinal column is numbered, and each number represents a section of the spinal cord's associated nerves.
What results in thoracic pain?Inflammation of the thoracic spine's muscles or soft tissues is the most typical cause of thoracic back pain. There are several causes of this inflammation, including abrupt sprains or strains (as in car accidents or sports injuries). slouching while standing or sitting over time.
To know more about Thoracic visit:
https://brainly.com/question/1656972
#SPJ4
In the light reactions, what is the initial electron donor? Where do the electrons finally end up?
Which type of cell has a cell wall?
A. Human skin cell
B. Animal cell
C. Fungi
D. Virus
Answer: Fungi
Explanation:
(Explanation from samiyah83)
Examples of organisms with cell walls are plants, fungi, protists (particularly molds and algae), and most bacteria (a few exceptions are mycoplasma and L-form bacteria) have cell walls. Animals and heterotrophic protists do not have cell walls.
huntington's disease is caused by a dominant allele (h) at an autosomal gene. the disease causes neurodegeneration, and people that have it often die at a young age. you are studying a population and find that the frequency of genotype hh is 0.09. what change might you expect to see in this population over time?
The Huntington's disease is caused by autosomal dominant mutation in HTT gene.
Frequency of genotype HH = 0.09 as H is mutant allele, hence in the population gene frequency change over time.
Huntington's disease is a progressive brain sickness due to a faulty gene. This disease reasons adjustments within the vital region of the brain, which have an effect on motion, mood and wondering talents. An inherited situation wherein nerve cells within the brain wreck down over the years. It normally starts off evolved in a person's 30s or 40s. Commonly, Huntington's disorder consequences in innovative motion, thinking, and psychiatric signs. No therapy exists, however capsules, bodily remedy, and talk remedy can help manipulate some signs.
The price of disorder progression and duration varies. The time from the first symptoms to loss of life is regularly about 10 to 30 years. Juvenile Huntington's disease generally outcomes in death inside 10 years after symptoms increase.
There may be presently no therapy for Huntington's disease or any manner to stop it getting worse. but remedy and assist can help reduce some of the issues it causes, such as: temper swings and involuntary movements. Occupational therapy to help make ordinary obligations less complicated.
Learn more about Huntington's disease here:- https://brainly.com/question/17465455
#SPJ4
Compare the concentrations listed in the table for methadone and phenobarbital. Which concentration is higher? By how much?
Combining methadone with drugs that depress the central nervous system, such as phenobarbital, can have severe adverse effects, including breathing difficulties, unconsciousness, and even death.
What is methadone?Methadone is a drug that the Food and Drug Administration (FDA) has licensed for both pain management and medication-assisted therapy (MAT) for opioid use disorder (OUD). Methadone is a safe and reliable drug when used as directed.
Methadone assists people in achieving and maintaining recovery as well as reclaiming active and fulfilling lives. A complete treatment program that combines counseling and other behavioral health therapies in order to provide patients with a whole-person approach also incorporates methadone as one of its components.
Therefore, combining methadone with drugs that depress the central nervous system, such as phenobarbital, can have severe adverse effects, including breathing difficulties, unconsciousness, and even death.
Read more about methadone, here
https://brainly.com/question/3265912
#SPJ4
How is habitat disturbance absolutely necessary for the long-term survival of the woodpecker?
The habitat destruction leads to urbanization and increase in richness of woodpecker species.
In urban settings, woodpeckers are relatively frequently recorded. Their habitat preferences and the habitat quality of the territories found in an urban matrix are not, however, thoroughly investigated. Urbanization may lead to the depletion of dead wood resources, which are essential for the existence of woodpeckers. Dead wood resources, which generally took the form of dead tree limbs, were a key factor in the richness of a society.
Municipal greenery offers very few dead wood supplies, hence woodpeckers stayed away from this type of habitat. Studies revealed a correlation between species abundance and the availability of dead wood and canopy covering. According to certain research, less tended urban green spaces are essential for the presence of woodpeckers, and management of urban greenery is a significant factor that affects woodpecker assemblage.
Learn more about woodpeckers here;
https://brainly.com/question/16398763
#SPJ4
Which best describes the role of communication in scientific investigations?
O Communication can help identify good scientific questions to further investigate.
O Communication is not necessary once the data are collected because the scientists can d
themselves.
O Communication should not be used in planning the experimental design because the scien
ideas.
O Communication is important because the scientists need to convince other researchers not to challenge their results
Answer:
Communication can help identify good scientific questions to further investigate.
Explanation:
The flaplike opening in the interatrial septum of the fetus through which blood is shunted from the right to the left atrium is the?
The flaplike opening in the interatrial septum of the fetus through which blood is shunted from the right to the left atrium is the foramen ovale.
What is Patent foramen ovale?Patent foramen ovale can be described as the flaplike opening that is been found in between the atrial septa primum and secundum .
This is been located at the at the fossa ovalis and do persists after age 1 year, it should be noted that foramen ovale serves as a physiologic conduit , hence The flaplike opening in the interatrial septum of the fetus through which blood is shunted from the right to the left atrium is the foramen ovale.
Find out more on the fetus at https://brainly.com/question/7485706
#SPJ1
If a culture of liver cells were deprived of amino acids, which category of macromolecule would the liver cells not be able to construct properly?.
The liver cells wouldn't be able to produce the macromolecules in the protein category adequately.
Describe a macromolecule:A macromolecule, such as a protein or nucleic acid, is a very big molecule crucial to biophysical processes. It is made up of many atoms that are covalently bound. The smaller molecules known as monomers are the building blocks of many macromolecules. More atoms make up macromolecules than there are in regular molecules.
What is the function of macromolecules?The job of macromolecules is to sustain structures. act as a repository for fuel to maintain and retrieve genetic data.
What is an example of a macromolecule?Proteins, nucleic acids, and polysaccharides are typical examples of macromolecules.
To know more about Macromolecule visit:
https://brainly.com/question/15237842
#SPJ4
the white matter of the spinal cord contains . group of answer choices myelinated nerve fibers only unmyelinated nerve fibers only myelinated and unmyelinated nerve fibers soma that have both myelinated and unmyelinated nerve fibers
Option A: the white matter of the spinal cord contains myelinated nerve fibers only.
The central nervous system (CNS) comprises the brain and spinal cord. It generally contains two types of tissues: white matter and gray matter. White matter appears pinkish white while the gray matter is a darker hue. White matter is located in the outer regions of the CNS while the gray matter is located closer to the CNS.
The white matter of the central nervous system consists of myelinated nerve fibers. This further means that it contains axons that are covered by a protected covering of myelin. The characteristic color of white matter is acquired from myelin which is generally made up of lipid tissue. Myelin protects the nerve fibers from any injury.
The white matter of the spinal cord is composed of axons that are covered by myelin. The primary function of white matter is to coordinate and signal a to and fro motion between the brain and the spinal cord.
To know more about the white matter of the spinal cord, refer to the following link:
https://brainly.com/question/15865410
#SPJ4
s a pinpoint depression in the occlusal surface of a posterior tooth where two or more grooves meet.
Pit is a pinpoint depression in the occlusal surface of a posterior tooth where two or more grooves meet.
Occlusal surface is one of the various surfaces of the teeth. It is associated with the chewing. The occlusal surface consists of the premolars and the molars. They are the most commonly used teeth and hence are more prone to wear and tear.
Pits is actually the depression in the enamel layer of the teeth. It is more commonly seen in the premolars and molars as they are more used on daily basis. These may be formed due to bacterial activity in the teeth.
To know more about occlusal surface, here
brainly.com/question/12857769
#SPJ4
question which hormones does the body release under stress? estradiol and luteinizing hormone estradiol and luteinizing hormone estrogen and progesterone estrogen and progesterone epinephrine and norepinephrine epinephrine and norepinephrine insulin and prolactin insulin and prolactin
epinephrine and norepinephrine hormones the body release under stress
What hormone produced by the adrenal gland is involved in the stress response?The adrenal medulla, the innermost region of the adrenal gland, regulates the chemicals that trigger the flight or fight response. The adrenal medulla secretes two primary hormones: epinephrine (adrenaline) and norepinephrine (noradrenaline), which have comparable roles.
Cortisol is known as the stress hormone because it is implicated in stress responses. It raises blood sugar, raises blood pressure, and lowers immunological responses.
Cortisol influences various parts of your body, primarily regulating your body's response to stress.
learn more about adrenal gland refer
https://brainly.com/question/1406904
#SPJ4
Answer: epinephrine and norepinephrine hormones the body release under stress
Explanation: When brain go brrr, its makes these chemicals so brain can stop going brrr.
PLEASE HELPP MEE!!!!!!!
A beaker contains a mixture of sand and salt. A student adds water to dissolve the salt. Which processes can be used to separate out the sand and the salt?
A- Filtration to collect the sand and displays too. To collect the salt
B- Filtration to collect both sand and the salt
C- Dislatation to collect the sand and filtration to collect the salt
D- Dislatation to collect both sand and salt
The process that can be used to separate out the sand and the salt is filtration to collect the sand and displays too. The correct option is A.
What is filtration?Separating solid from liquid particles is done through filtration. A filtration paper separates them, keeping the liquid filter in the beaker and the solid particles in the paper.
Here, sand and salt are combined in a beaker. The leftover sand will be filtered from the paper after the remaining water and salt have been added to it.
Thus, the correct option is A. Filtration to collect the sand and displays too.
To learn more about filtration, refer to the link:
https://brainly.com/question/28619644
#SPJ1
Regular distribution is observed for many organisms due to _______. a. the need to maximize exposure to sunlight b. the need to avoid predators c. interactions between individuals d. the plentiful availability of water please select the best answer from the choices provided a b c d
Answer:
The answer is C.
Explanation:
hope this helps!!
The cell membrane is _______ (or selectively permeable), meaning it controls the passage of molecules in and out of the cell. p/orn
Answer: The answer is semipermeable
Explanation:
What is the purpose of all interactions among the components of a climate system?(1 point) to assist human activities such as shipping and farming to assist human activities such as shipping and farming to transport different species of animals around the globe to transport different species of animals around the globe to create various weather patterns on earth to create various weather patterns on earth to transfer thermal energy around the world
The main purpose of all interactions among the components of a climate system is to create various weather patterns on earth. So, the correct option is C.
The earth's surface is where several elements of the climate system come together. Modeling (or recreating) the climate system requires an understanding of its many sections or components.
This chapter outlines the fundamental elements of the Earth that make up the climate system, as well as the fundamental scientific concepts and vital procedures required to model each of these elements.
The Atmosphere, Ocean, Ice, and Land are some of these elements. Individual processes are often gathered into a model of one system component, with the climate system being depicted as a collection of building blocks.
To depict the overall climatic system, the components are connected to other components. The ability to construct a representation of the system, such as a climate model, depends on being able to comprehend and then depict the interactions between processes and between components.
To know more about climate system go to https://brainly.com/question/17350365
#SPJ4
comparative study of phrenic and intercostal nerve transfers for elbow flexion after global brachial plexus injury
Comparative study of phrenic and intercostal nerveGlobal brachial plexus injuries (BPIs) give out the result as devastating events frequently resulting in severe functional impairment. The widely used nerve transfer sources for elbow flexion in patients with global BPIs include intercostal and phrenic nerves.
The comparative study of the phrenic and intercostal nerve that transfers after global brachial plexus injury for purpose of elbow flexion is studied and the aim of this study was to do a comparison for elbow flexion after global BPI.
A retrospective review of 33 patients treated with phrenic and intercostal nerve transfer for elbow flexion in posttraumatic global root avulsion BPI was carried out. In the phrenic nerve transfer group, the phrenic nerve was transferred to the anterolateral bundle of the anterior division of the upper trunk (23 patients); in the intercostal nerve transfer group, three intercostal nerves were coapted to the anterolateral bundles of the musculocutaneous nerve.
The efficiency of motor function in the phrenic nerve transfer group was 83%, while it was 70% in the intercostal nerve transfer group.
For more information on phrenic nerves click on the link below:
brainly.com/question/7155835
#SPJ4
Which of the following is not a major activity of the stomach? a. mechanical digestion b. HCl production c. nutrient absorption d. enzyme secretion
c. nutrient absorption is not a major activity of the stomach
What is the stomach's main function?Acid and digestive enzymes are produced by the stomach. The stomach is lined with , which are ridges of muscular tissue. Periodically contracting, the stomach muscles churn the food to speed up digestion. Food can go from the stomach to the small intestine when the pyloric sphincter, a muscle valve, relaxes.
Propulsion—peristaltic smooth muscle contractions that move food from the fundus to the constricted pylorus—is how mechanical digestion happens in the stomach.
As the muscular layers in the stomach lining flex, a mixing and churning action is created, which is mechanical digestion.
learn more about digestive enzymes refer
https://brainly.com/question/11678128
#SPJ4
A chicken has 78 chromosomes in its somatic cells. How money chromosomes did the chicken inherit from each parent? How many chromosomes are in each of the chicken's gametes? How many chromosomes will be in each somatic cell of the chicken's offspring?
If a chicken has 78 chromosomes in its somatic cells, then it has inherited half the number of chromosomes from each parent i.e 39 from each parent. There are 39 chromosomes in each of the chicken's gamete. There will be 78 chromosomes in each somatic cell of the chicken's offspring.
The gamete cells divide by the process of meiosis whereas the somatic cells divide by the process of mitosis.
During the process of meiosis, the number of chromosomes is reduced to half. Hence, the gamete cells contain half the number of chromosomes as the somatic cells. If fertilization occurs, the other half of the number of chromosomes is inherited from the other parent. Hence, a chicken will inherit half the number of chromosomes from each parent.
Somatic cells in the body divide by the process of mitosis. The process of mitosis produces genetically identical copies. Hence, the chromosome number will remain the same i.e 78 in the somatic cell of the chicken's offspring.
To learn more about somatic cells, click here:
https://brainly.com/question/26509645
#SPJ4
group of students are conducting an experiment. Since potatoes contain both sugar and water, the students use them in the experiment. The students cut six equal cubes of potato and weigh them. They place the six cubes into six different beakers containing different concentrations of sugar solutions, then weigh each potato cube after 24 hours and calculate the percent change in mass. The graph below shows the result of their experiment.
Which of the statements below is a valid conclusion about this experiment?
a
The higher the concentration of sugar, the more likely the water concentration will be at equilibrium.
b
The lower the concentration of sugar, the more likely the potato will gain mass.
c
The higher the concentration of sugar, the more likely the potato will gain mass.
d
The lower the concentration of sugar, the less likely the potato will gain mass.
Answer:
the answer is B.
based on the graph, the higher the sugar concentration in the glucose solution, the more the potato strip loses mass. this is due to the net movement of water molecules out of the potato strip into the glucose solution of lower water potential. as such, the potato strip loses more mass if placed in a glucose solution of higher sugar concentration.
B is just the reverse: the lower the sugar concentration of the glucose solution, the more mass would be gained by the potato strip (due to the net movement of water molecules INTO the potato strip this time round)
hope this clears up!
Please answer the following questions as instructed
The physical or chemical changes that occur are as follows:
NaCl (Table Salt) dissolves in water- physical changeAg (Silver) tarnishes - chemical changeMilk sours - chemical changeAn apple is cut - physical changeHeat changes H2O to steam - physical changeBaking soda reacts to vinegar - chemical changeFe (Iron) rusts - chemical changeAlcohol evaporates - physical changeIce melts - physical changeSugar dissolves in water - physical changeWood rots - chemical changePancakes cook - chemical changeGrass grows - chemical changeA tire is inflated - physical changeFood is digested - chemical changePaper towel absorbs water - physical changeWhat are physical and chemical changes?Physical changes are changes that are easily reversible and in which no new substances are formed.
Physical changes involve:
a change in size, shape, or state no new substance is formedExamples of physical changes include
evaporation of water, dissolution of sugar in water.
Chemical change are changes that are not easily reversible and in which new substances are formed.
Chemical changes involve:
a change in the physical and chemical propertiesa new substance is formedExamples of chemical changes are rotting of wood, rusting of iron.
In conclusion, changes that new products are formed are chemical changes whereas changes that does not form new products are physical changes.
Learn more about physical changes and chemical changes at: https://brainly.com/question/17384175
#SPJ1
Snap dragon flower color displays incomplete dominance. Which is the likely phenotypic ratio of the f2 progeny resulting from a monohybrid cross of true-breeding parents with white and red flowers?.
The correct answer is 1 red : 2 pink : 1 white
A monohybrid cross is made up of two organisms that have distinct variants at the same genetic locus. In a monohybrid cross, the character(s) under investigation are controlled by two or more mutations at a single gene locus. Each parent is selected to be homozygous or true breeding for a particular characteristic in order to perform such a cross (locus). When a cross meets the requirements to be classified as a monohybrid cross, it is typically identified by a distinctive distribution of second-generation (F2) offspring, also known as the monohybrid ratio. A monohybrid cross is a cross between two homozygous individuals, which produces the opposite phenotype for a particular genetic characteristic.
To know more about monohybrid cross refer to https://brainly.com/question/22335423
#SPJ4
fecal transplant in children with clostridioides difficile gives sustained reduction in antimicrobial resistance and potential pathogen burden
It is true that Fecal microbiota transplantation (FMT) for CDI treatment in children reduces potential pathogen burden and antimicrobial resistance.
Fecal microbiota transplantation (FMT) also known as stool transplant, intestinal microbiota transplantation or bacteriotherapy is performed through a colonoscopy where the microbiota (healthy bacteria) from the carefully screened donor’s feces is transferred to the colon of the recipient.
Children with Clostridioides difficile infection (CDI) treated with fecal microbiota transplantation (FMT) have lower levels of potential pathogens and genes associated with antimicrobial resistance (AMR), as well as altered microbiota makeup and function. However, the acquisition of some AMR genes post-FMT and the low levels of possible pathogens discovered in donors imply that more research into the screening of donors using metagenomics sequencing prior to FMT is necessary.
Learn more about Fecal microbiota transplantation (FMT) here:
https://brainly.com/question/9869775
#SPJ4